The impetus for the Times piece was the landslide victory of Richard Mourdock over Richard Lugar in an Indiana Republican primary last week, which refocused attention on the rising influence of Tea Party-style conservatism in the upper chamber. Mourdock, if he’s elected, will join a bloc of Republican senators whose governing approach mirrors that of South Carolina’s Jim DeMint, the Tea Party’s de facto leader on Capitol Hill.

To promote unity within his ranks and to secure his grip on power, it’s important for McConnell to respond to his party’s evolution toward the DeMint/Tea Party style, something he’s been doing lately. The problem, though, is that this style severely constrains his ability to exercise the traditional prerogatives of a Senate leader and threatens to render him the upper chamber’s equivalent of John Boehner, who lives with the knowledge that any deal-making with the other side could spur an intraparty coup.

This reflects an important point about Tea Party Republicanism: It isn’t really about ideology; it’s about governing tactics.

After all, the battle for the Republican Party’s ideological soul was fought and settled decades ago. In the late 1970s, a movement somewhat similar to the Tea Party gave rise to a number of primary challenges to sitting GOP senators. The targeted incumbents, though, were genuine liberals – New Jersey’s Clifford Case, Ed Brooke of Massachusetts, and New York’s Jacob Javits. The Republican Party of that era was in the midst of a sweeping geographic and demographic evolution, one that established it as the home for white Southerners and newly mobilized evangelical Christians and left the old Rockefeller wing extinct. When Ronald Reagan triumphed in 1980, it certified the GOP as the conservative party it remains today.

The primary challenges of the current Tea Party era are not defined by similarly vast ideological gulfs. Lugar, for instance, was generally a party man in his Senate votes, racking up a fairly conservative record and voting against President Obama’s major domestic initiatives. But he did leave some room for independence and compromise, particularly in his specialty area of foreign policy. His opponent, Mourdock, was to Lugar’s right on some issues, but what really distinguished him is his belief that the Senate is a venue for partisan warfare.

“Bipartisanship,” Mourdock declared last week, “ought to consist of Democrats coming to the Republican point of view.”

This is as concise a distillation of the Tea Party’s governing vision as you’ll find. It’s not really about moving the GOP to the right; the party is already there, and has been for a while. It’s about reflexively opposing the other party on every issue, resisting compromise at all costs, and exploiting every available legislative tool to stymie the other side. This mind-set is already pervasive in the House, and as the Times story shows, it’s now making its way into the Senate.

The lesson that Lugar’s defeat sends to individual Republican senators is that they risk the same fate if they don’t get with the Tea Party program. Traditionally, there’s been room for them to carve out a specialty area – like Lugar with foreign policy – and to reach across the aisle to advance legislation that affects it. But that model is fast giving way to the Tea Party’s expectation of relentless, 24/7/365 partisan warfare.

A case study in how this works can be found in Orrin Hatch, who was spooked when his Utah colleague Bob Bennett was denied renomination in 2010. Hatch’s voting record is reliably conservative, but he has (or had) a reputation as a deal-maker. When Bennett went down, though, Hatch swore off compromise and recast himself as a Tea Party-friendly partisan warrior. It will probably be enough to save his job, which only reinforces the message of Lugar’s defeat.

All of this affects what McConnell is, and isn’t, able to do as the GOP’s leader. In the past two years, he’s played a crucial role in resolving standoffs with the White House that House Republicans instigated – over the debt ceiling last summer and expiring payroll taxes before Christmas. But his ability to keep doing this depends on having space to negotiate and cut deals with Democrats, and with every Tea Party primary triumph, that space erodes a little more.

The Senate is not the House yet, but the Tea Party is pushing it in that direction. As Norm Ornstein and Thomas Mann explain in their new book, the principles of a parliamentary system – absolute party loyalty and reflexive, unyielding opposition from the out-of-power party – are coming to define Capitol Hill. For McConnell, this will force a personal reckoning over whether he’s comfortable functioning as the kind of leader such a system demands. For the rest of the country, it will force a different kind of reckoning, as the total incompatibility of the parliamentary style with the American system becomes apparent.

And if anything, this understates the degree to which filibustering has become an everyday tool; how often have Reid and Democrats not even bothered to file cloture on bills, knowing they lacked the necessary 60 votes and not wanting to waste precious days of precious Senate time?

Faced with yesterday’s Republican maneuver, an exasperated Reid took to the Senate floor and said, “If there were anything that ever needed changing in this body, it’s the filibuster rules, because it’s been abused, abused, abused.”

He also invoked the names of two of his Democratic colleagues, Tom Udall and Jeff Merkley, who attempted before the current Congress convened in January 2011 to sell their party on what they called the “Constitution option” – under which Democrats would exploit a technicality to change Senate rules on the first day of the new session with a simple majority vote, not the two-thirds supermajority normally required. Merkley and Udall weren’t actually proposing to get rid of the filibuster; the new rules they envisioned would just have stopped the mere threat of a filibuster from killing a bill and forced senators to engage in “real” filibustering. But the ultimate ability of the minority party to kill legislation it doesn’t like by forcing proponents to secure 60 votes would have stood.

As benign as their plan was, it still prompted an outcry from the right and was regarded as too extreme even by some Democratic senators. In the end, Reid struck an agreement with Mitch McConnell, his Republican counterpart, that made some very modest and superficial reforms – an agreement that, as Reid’s frustration yesterday demonstrated, didn’t change much.

“If there were ever a time when Tom Udall and Jeff Merkley were prophetic, it’s tonight,” Reid said in his floor speech yesterday. “These two young, fine senators said it was time to change the rules of the Senate, and we didn’t. They were right. The rest of us were wrong — or most of us, anyway. What a shame.”

The question is whether Reid’s outburst signals a real shift in his thinking, or if he was simply blowing off steam (or trying to gain some leverage with Republicans by flirting with rules reform). In the near-term, it doesn’t really matter. if filibuster rules are going to be changed, it will almost certainly be at the start of a Senate session, not in the middle of one, so the earliest Democrats would move on anything is next January. And with all of the vulnerable Democratic seats up this fall, there’s a real chance they won’t be running the Senate next January, anyway.

That said, there’s another big development this week that increased the Democrats’ chances of holding on to the Senate — and their incentive for changing the rules if they do: Richard Lugar’s primary loss in Indiana.

With Indiana Republicans now saddled with a far-right candidate, Richard Mourdock, Democrats have a real opportunity to pick up Lugar’s seat. If they succeed, it will radically diminish the GOP’s odds of reclaiming the chamber.

But even if Mourdock goes on to lose in the fall, his primary triumph ensures that Senate Republicans will be even more ideologically inflexible, compromise-resistant and filibuster-dependent going forward. The threat that they’ll suffer the same fate as Lugar (and the other Republican congressional incumbents and establishment favorites who went down in the 2010 primary season) will hover over every vote that every GOP senator takes.

So if Reid really has had it with the filibuster, next January may be a good time to do something about it, because the problem isn’t going to get any better. Of course, if divided government is still the rule next year – a Democratic White House and Senate and a Republican House, say – then any filibuster reforms wouldn’t have much practical effect on the enactment of laws. But the Merkley-Udall proposal could be a good starting point, a means of reestablishing the precedent for filibuster reform and laying the groundwork for a more sweeping overhaul at a later date.

If they were playing their assigned roles, it would have been Obama leading the way on same-sex marriage this week, issuing an eloquent call for equality that would prompt Biden to come around too. Instead, it was the vice president who made the first move, making a surprise declaration on Sunday that he’s “absolutely comfortable” with gay marriage and setting off a 72-hour media frenzy that culminated in Obama finally admitting in public that “I think same-sex couples should be able to get married.”

There’s some obvious political logic to this role reversal, which has helped fuel speculation that the events of the past few days were all part of an orchestrated White House rollout: Biden launches a trial balloon on Sunday, Education Secretary Arne Duncan ups the ante on Monday, until finally it’s safe for Obama to make the leap that his base has been expecting him to make for years.

But as conspiracy theories go, this one’s a bit hard to swallow. For one thing, Biden wouldn’t have addressed gay marriage on “Meet the Press” unless David Gregory had brought it up, and little about Duncan’s statement on “Morning Joe” the next day suggests it was anything but a spontaneous response to an unexpected question (a question that was almost drowned out by one of the show’s hosts). And the insider accounts of the White House’s deliberations that are now emerging all suggest that Biden’s comments were unscripted and forced Obama to dramatically speed up his timetable for confronting the marriage question.

This puts Biden in an unlikely role: hero to the left – the man who gave Obama no choice but to say what he’s been scared to say since taking the national stage. As Ana Marie Cox remarked on Twitter Wednesday afternoon, “I applaud the leadership of President Biden.”

What exactly prompted Biden to speak out the way he did on Sunday remains unclear. If you put aside the notion that the White House instructed him to do so, it’s possible Biden was simply speaking from the heart, motivated by his own interactions with gay couples and their children. It’s also possible that his candor was accidental, a botched effort to mimic Obama’s tortured rhetoric about “evolving” on gay marriage without actually endorsing it.

Whatever his motive, Biden has clearly sped up history. It’s long been assumed that Obama considered the issue too risky to address before this year’s election, although some unnamed advisors are now telling the New York Times that he was going to get to it by the fall. Either way, there’s every reason to believe that the only reason Obama took such a bold step on Wednesday is because of what Biden did on Sunday.

At the very least, this makes Biden a major figure in what will go down as one of the Obama administration’s signature moments, guaranteeing that his vice presidency will be remembered in history – something that can’t be said for many of his predecessors. But this also has the potential to generate newfound respect and appreciation for Biden among the younger, more culturally liberal party base, voters who until now have been conditioned to regard Biden as an almost comic figure – the tone-deaf, gaffe-prone great-uncle of American politics.

For a 69-year-old vice president who still has hopes of winning the top job for himself someday, this is surely a welcome development.

Right on cue when Mourdock’s win was announced, the Democratic Senatorial Campaign Committee released a statement calling him “this year’s Ken Buck” – a reference to one of the Tea Party-aligned Republican Senate candidates in 2010 whose fringe image cost the party a winnable race. This may be wishful thinking, though. Mourdock has a limited profile in Indiana, but he has solid credentials and has won statewide office before (he’s current the state’s treasurer); it’s just as likely he’ll prove to be this year’s Pat Toomey, a similarly credentialed Tea Party candidate who managed to win Pennsylvania’s 2010 Senate race.

In the days ahead, there will be countless tributes to Lugar from his colleagues and from commentators, who will salute his seriousness, civility and willingness to work across party lines. Actually, it’s already begun, with John Kerry releasing a statement as the votes came in calling Lugar’s defeat a “tragedy.”

There’s something to this, especially when it comes to foreign policy and arms control, subjects that Lugar devoted himself to in the Senate, but it’s also easy to get carried away. Lugar’s independence had its limits, and his voting record has been reliably conservative and Republican over the years. He’s no Jim DeMint, but he’s also not an Arlen Specter.

This gets to the real significance of the Indiana result. Lugar’s loss is a blow to the Senate not so much because he’ll be absent from it starting next January but because of the lesson that the Republicans who remain will take from it. The rules and traditions of the Senate, after all, have long encouraged senators to conduct themselves as Lugar has, remaining generally loyal to their party but also exercising individual prerogatives as they see fit. But the GOP’s conservative base has in the Obama era risen up against this approach and launched a relentless campaign to turn the party’s Senate and House ranks into a uniform bloc of ideologically “pure” partisan warriors.

That campaign was wildly successful in 2010, when conservative challengers – many of whom would previously have been written off as crackpots and condemned to also-ran status – scored a series of high-profile primary season victories over Republican incumbents and Republicans with strong establishment credentials and ties. Like Lugar, most of the Republicans who went down were hardly moderates or liberals; they were standard-issue conservatives whose sins consisted of one or two wrong votes on major bills, or too much friendliness toward Obama and Democrats, or too much of an association with the party establishment. Think of Utah Sen. Bob Bennett, who was trounced at the state’s GOP convention, or South Carolina Rep. Bob Inglis, who was crushed in a primary.

It’s impossible to overstate the traumatic effect that 2010 had on the way Republican members of Congress approached their work. Many of the newly elected senators and House members were true believers, as were a fair number of Republicans already in the House and Senate. But there remained many legislators like Lugar, who had in the past been willing to occasionally break with their party and work with the other side. 2010 was a clear message to these senators and House members that they risked suffering the Bennett/Inglis fate if they didn’t change their ways.

Most got the message. A prime example is Orrin Hatch, Bennett’s Utah colleague and a man whose Senate service began the same year as Lugar’s, 1977. For the past two years, Hatch has embraced – or re-embraced – unrelenting and vitriolic partisan warfare, hurling insults at the White House and Democrats and catering to the conservative base’s siege mentality. Hatch is up this year too and was in grave danger of losing his party’s support, but his transformation appears to have saved him; he won the Utah GOP convention by 18 points a few weeks ago.

2010 clearly had some impact on Lugar. His voting in the Senate became more conservative and his posture toward Obama – whom he’d gone out of his way to praise on foreign policy in the 2008 campaign – became more hostile. But he would only go so far, and resisted the complete makeover that Hatch put himself through. Whether this was a principled stand or simply a miscalculation is a matter of opinion, but it didn’t take long for Lugar to release a statement on Tuesday night bluntly spelling out his objections to the approach to legislating that Mourdock and his wing of the party represent:

He and I share many positions, but his embrace of an unrelenting partisan mindset is irreconcilable with my philosophy of governance and my experience of what brings results for Hoosiers in the Senate. In effect, what he has promised in this campaign is reflexive votes for a rejectionist orthodoxy and rigid opposition to the actions and proposals of the other party. His answer to the inevitable roadblocks he will encounter in Congress is merely to campaign for more Republicans who embrace the same partisan outlook. He has pledged his support to groups whose prime mission is to cleanse the Republican party of those who stray from orthodoxy as they see it.

In Utah, Hatch has gone out of his way to convince Republicans that he embodies this philosophy. He still has to get through a primary next month, but assuming he does, Hatch’s survival and Lugar’s defeat will probably have the same effect on Republicans in the next Congress that the 2010 primaries had on Republicans in this one.

For Democrats, the promise of Barrett’s candidacy is that his pleasant manner and lack of sharp ideological edges will make it difficult for Walker to turn the tables and transform the June 5 vote into a referendum on the Democratic Party and its nominee. That Barrett is generally seen as more moderate than Falk and that he’s run without the support of Wisconsin’s most powerful labor unions could also make it tougher for Walker – who is armed with record-shattering financial resources – to attack him as an ideologue beholden to special interests.

He is, in other words, a logical vehicle for a party that wants the general election to be all about the incumbent, and nothing else, which pretty much explains why Barrett leads the endorsement game. This insider consensus may well be right, and Barrett – if he does secure the nomination today – might very go on to knock off Walker next month.

But Wisconsin Democrats could be taking more of a chance here than they appreciate. The basic problem: Barrett has some potentially significant general election liabilities, but because of the unique circumstances of this year’s race, they haven’t been explored and tested during the primary campaign.

This is a result of the immense pressure that Democratic leaders and activists placed on both candidates to shy away from aggressive attacks that might create lingering divisions within the party and to focus their fire on Walker and the GOP agenda. Functionally, this pressure has constrained Falk more than Barrett, since she’s been running from behind; front-runners like Barrett generally have no problem with all-positive campaigns.

The main issue with Barrett’s candidacy is that he actually utilized the collective bargaining reforms that Walker and the GOP enacted – reforms that were passed under ferocious Democratic objections and that triggered the recall effort – to impose concessions on his city’s employees last summer. This, obviously, will become a prime pro-Walker talking point if Barrett is the Democratic nominee. In fact, it already is. As the conservative Weekly Standard wrote a few weeks ago:

[B]arrett’s actions speak louder than words. The fact that he proposed–and used–limits on collective bargaining in order to save the city money proves the point that public sector unions use collective bargaining to prevent changes to their costly benefits.

Barrett has a response ready. State aid to Milwaukee was radically slashed by Walker and his GOP allies, his camp is quick to note, and with no way to make up for it with property tax revenue he was forced to choose between mass layoffs and employing Walker’s law. It’s a choice that no municipal leader should have to make, the line goes, and Barrett has publicly committed himself to repealing the ban on collective bargaining.

Will this pass the sniff test with voters? Or will it bolster Walker’s claim that his actions have been vital to the state’s fiscal health – and aren’t part of a radical ideological agenda, as Democrats charge? The answer is far from clear, and the primary campaign is a big reason why.

Under ordinary circumstances, Falk and her allies would have loudly raised the issue, in campaign literature, television ads, speeches, debates, and interviews. But this is no ordinary campaign. Among Democratic leaders, there is hyperawareness of the challenges involved in beating Walker – and absolutely no appetite for a civil war. Under these circumstances, Falk risked inciting a loud and damaging backlash from neutral Democrats if she launched a direct attack on Barrett.

Apparently, that risk was too much for her. A few weeks ago, she debuted an ad that drew a clear but still unspoken contrast with Barrett over collective bargaining. It was supposed to mark the start of a stepped-up attack on the front-runner, one aimed at closing the gap and pushing Falk over the top in the race’s closing days. But Barrett’s backers warned her off by playing the party unity card, and nothing much came of it. Falk’s home stretch ads have been positive, as have the spots bankrolled by her labor allies. Nor did she go after Barrett in the final debate of the campaign, held last Friday night.

So it’s not surprising that Barrett has maintained his lead and seems poised to win today. Again, this may not end up mattering in June; Barrett may prove to be a perfectly fine candidate. But the knock on him, besides the collective bargaining issue, is that he’s just too nice a guy and too laid back and that he might get pushed around too easily by Walker and his crew. That concern has not been allayed by his race against Falk.