The impetus is the surprise victory of Deb Fischer, a little-known state legislator, over two seasoned opponents in Tuesday’s Nebraska Republican Senate primary. Fischer’s candidacy seemed dead in the water until about a week ago, when she was endorsed by Sarah Palin. A last-second ad blitz from a super PAC controlled by the founder of Ameritrade added to her momentum, and Fischer ended up beating out state Attorney General Jon Bruning, who had been the favorite, by 5 points.

The outcome was greeted with immediate joy by Democrats, with the DSCC putting out a statement calling Fischer an “untested” and “accidental” nominee for the seat being vacated by Democrat Ben Nelson. The hope for Democrats is that the 61-year-old Fischer, who has represented a rural western Nebraska district in the state Senate since 2005, will melt under the spotlight of a high-stakes general election contest – much the way Sharron Angle, Christine O’Donnell, Ken Buck and Joe Miller did in 2010.

This may prove to be wishful thinking. Fischer could end up being a perfectly competent candidate, one who isn’t prone to erratic behavior and pointlessly inflammatory rhetoric and who doesn’t have any serious skeletons in her closet. Certainly, she showed strong communication skills in her acceptance speech Tuesday night. And because of Nebraska’s deep red shading and its particular antipathy toward Democrats in the Obama era, Fischer’s margin for error is probably substantial. The same mistakes that derailed Angle in Nevada may only be the difference between, say, a 20- and 10-point win in Nebraska.

That said, Fischer absolutely is an untested candidate. Bruning and the race’s other major candidate, state Treasurer Don Stenberg, spent months firing shots at each other and gobbling up all of the attention. The intensity of their battle probably helped create the opening that Fischer seized, but the late timing of her surge also spared her from facing much in the way of media scrutiny or attacks from her rivals. She raised and spent very little money, and not much is known about her.

For Democrats, that’s reason to cheer. Had Bruning (or even Stenberg, a veteran of eight previous statewide campaigns) won the primary, the general election race would have been a snore. Polls showed both men comfortably ahead of the Democratic candidate, former Sen. Bob Kerrey, who won elections in the state in 1982 (for governor), 1988 and 1994, back when he was something of a local hero. But Kerrey spent the last decade running the New School in New York and hasn’t been on a Nebraska ballot in 18 years. Partisan divisions have hardened since then, and Kerrey now faces cries of carpetbagging.

There are no meaningful Fischer/Kerrey poll numbers out yet. Presumably, the GOP nominee will begin with a solid lead, just because this is Nebraska (and because right now she embodies a neat underdog story). The question is how she’ll hold up, and on that score there’s some real doubt, which means that Nebraska is in play, at least provisionally.

Add in Indiana, where the Tea Party-aligned Richard Mourdock knocked off Dick Lugar last week, and two GOP primaries in one week have resulted in a surprise general election opportunities for Democrats. And primary season isn’t over yet. As Josh Kraushaar notes, the GOP’s grass roots seem poised to rise up against former Gov. Tommy Thompson in Wisconsin; that race is already considered a tossup, but a weak GOP nominee could tip the scales.

Other developments over the last year have also bolstered Democrats’ chances of holding the Senate, including the emergence of Elizabeth Warren in Massachusetts (her recent troubles notwithstanding), Olympia Snowe’s unexpected retirement in Maine, and encouraging news from Arizona and maybe even North Dakota. What looked like an awful Senate map for Democrats at the start of this cycle has come to seem more manageable – even more so after Tuesday night’s shocker in Nebraska.

In this narrative, the GOP didn’t mismanage the economy into the deepest downturn since the Great Depression. Rather, the economic crisis simply happened, ex nihilo, and Obama did nothing to stop or mitigate it. What’s more, he made things worse, with government spending and an explosion of debt.

The problem for Obama, as Bouie points out, is that there’s real appeal to this story. The electorate tends to exist perpetually in the present tense, with little collective memory or foresight. Republicans began banking on this the moment Obama was sworn in: Just stand against everything he’s doing, and if the economy remains in rough shape, sooner or later the public will hold him responsible, just because he’s the guy in charge. As it turned out, it took only about nine months for Obama’s approval rating to fall under the 50 percent mark, and it’s hovered around there ever since, putting him in danger of losing this fall.

One way the Obama campaign is attempting to counteract this is by challenging Romney’s own economic and job-creation credentials. The presumptive GOP nominee has been relentlessly touting his business (and not government) experience, hoping that voters will assume he knows how to fix the economy because of his private sector success. Polls suggest voters are buying it, at least to a degree, with Romney generally outpacing the president by several points on which candidate would be better on creating jobs and boosting the economy. This is the reason Obama’s campaign unveiled a brutal two-minute attack ad yesterday on Romney and Bain Capital on Monday; the idea is to convince voters that there’s not necessarily a connection between making money in business and understanding how the economy works.

It’s hard to say whether this will work. Romney is fighting back by highlighting jobs that were created through Bain and with a new video that tells the stories of struggling Americans who have been victimized by “the Obama economy.” As Greg Sargent explains, the video is a perfect reflection of both the misleading simplicity of Romney’s message and its potential effectiveness. There’s just a lot the Romney campaign can say and do to deflect from the impact of the Bain attacks.

In this way, Bush’s very brief reemergence today raises the question of whether Obama ought to be invoking his predecessor more frequently and more explicitly, and to make him a more central figure in the campaign. Polls show that voters still remember what happened on Bush’s watch and still hold him responsible for at least some of the country’s current problems. Obama does frequently make reference to what he inherited, and to the failure of the GOP to come up with a new economic platform during its White House exile. But more than anything else, it seems that Romney’s campaign fears being tied to Bush. And Bush, as his elevator trick shows, is willing to help them out by remaining inconspicuous. If Obama’s team wants it, there’s some slack to be picked up.

Which can be a problem in the Tea Party era. Conservative leaders and voters today aren’t as easily satisfied as they once were by candidates who are with them on paper. They want proof of absolute commitment to the cause – reason to believe that a would-be senator won’t ever compromise away a single conservative principle, no matter how much pressure is coming from party leaders, polling and the press. And Bruning, who has had to contend with revelations about his personal investments in state-regulated businesses and his purchase of a summer home with two executives from a company that the AG’s office had previously sought to help, doesn’t really have the image of a true believer.

Until very recently, Bruning’s main challenger for the GOP nomination was supposed to be Don Stenberg, the current state treasurer and a former attorney general. Backed by some serious money from the Club for Growth, Sen. Jim DeMint’s Senate Conservatives Fund and FreedomWorks, Stenberg has been portraying himself as the candidate of purity and pounding away at Bruning. But Stenberg, a veteran of three failed Senate bids and two other statewide offices, is something of a perennial candidate, and he lacks the freshness and outsider credentials that Tea Party conservatives tend to respond to. Thus did Bruning still seem poised to win the primary … until last week.

That’s when Palin came through with a surprise endorsement of the third candidate in the race, Deb Fischer, whose personal story is the most naturally appealing to the Tea Party crowd. The 61-year-old didn’t enter politics until 2004, when she won a seat in the state Senate, and on the campaign trail plays up her work as a rancher. She doesn’t ooze the same ambition as her opponents, and of the three candidates she’s the most likely to be immune to Potomac Fever.

The Palin announcement offered a huge jolt of momentum to Fischer’s effort, and was followed a day later by an endorsement from 1st District Rep. Jeff Fortenberry. Then, over the weekend, came one more surprise: a last-minute $200,000 ad buy from a super PAC that has decided to promote Fischer, and savage Bruning.  (The super PAC is run by Ameritrade founder Pete Rickets, whose son, Pete, defeated Stenberg in the 2006 GOP Senate primary.)

Where, exactly, the race stands in hard to say. Fischer’s campaign has been promoting internal polls that show her leapfrogging Stenberg and threatening Bruning for the lead. There hasn’t been a reputable public poll since earlier in the race, when Bruning was still the runaway favorite.

The national implications are twofold. If Fischer does manage to win, Nebraska could actually emerge as a Senate battleground this fall. With Democrat Ben Nelson declining to seek reelection, the seat has long been assumed to be an automatic Republican pickup, even after Bob Kerrey, a one-time governor and senator, decided to return to the state and launch a comeback bid. Polls have shown Kerrey getting trounced by Bruning – and with Barack Obama on course to lose the state by at least 20 points, it’s not as if Kerrey is going to get any help from the top of the ticket.

Fischer, though, would be a wild card. She’s largely untested, and there’s a lot that isn’t known about her background and her skills as a candidate. If she wins the nomination, she might do fine in the general election, but there’s also the chance she’d prove to be another Sharron Angle. And, of course, it could be that she does turn out to be the next Angle, and that it still doesn’t matter, given Nebraska’s partisan bent. (It’s doubtful that a Stenberg win would do much to help Kerrey, since he’s a more established figure and has been able to win before.)

The bigger consequence of a Fischer win, though, would be to reinforce the message that was sent to Republican senators by last week’s Indiana Senate primary, when Dick Lugar was trounced by his Tea Party-aligned challenger. As I wrote yesterday, the Tea Party movement really isn’t about making the GOP a more conservative party; it’s about making what is already a conservative party more obstinate, unyielding and hostile to Democrats. A surprise victory by Sarah Palin’s candidate today would help that cause.

But outside of that ’94 primary, every time Romney has been in a competitive race, an opponent has accused him of making his fortune by gutting companies and ruining the lives of innocent workers.

The new Obama ad, which is airing in Virginia, Pennsylvania and Colorado, focuses on the story of GST Steel, a company in which Bain purchased a majority stake in 1993, just before Romney’s first foray into politics. In 2001, after Romney had left his day-to-day role with Bain and was overseeing the Olympics in Utah, GST’s Kansas City plant was shuttered, costing more than 700 workers their jobs even as Bain itself profited. The ad mixes in clips of Romney boasting about his job creation record and empathy for the jobless with testimonials from those whose lives were affected by the plant’s closure.

“It was like a vampire,” one former GST employee says of Bain. “It came in and sucked the life out of us.”

It’s a dramatic, well-produced ad that paints a damning portrait of the presumptive GOP nominee and the firm he built. The question is whether it will be effective, and the track record for previous Bain assaults on Romney is mixed:

1994 Senate general election: Here is the example the Obama team is hoping to emulate. After his September ’94 GOP primary win, a poll gave Romney a narrow edge over Ted Kennedy, whose own popularity had waned in the wake of the William Kennedy Smith trial. By the end of the month, the Kennedy campaign settled on Bain as Romney’s prime vulnerability, and made the firm’s acquisition of an Indiana company, SCM, a major point of emphasis. Here is one of several SCM ads that Kennedy’s campaign ran:

Interestingly, when this assault began, the Boston Globe noted that Romney had been running warm and fuzzy ads about his personal story for a few months and suggested that “voters may see this series as the powerful Kennedy machine beating up on that nice young man.” But by early October, Kennedy was comfortably ahead again, and the race wasn’t close the rest of the way, with the incumbent prevailing by 17 points. Were the Bain spots responsible for the giant polling shift? It’s impossible to say for sure, but they clearly didn’t hurt.

2002 gubernatorial general election: Romney spent much of the fall campaign running behind the Democratic nominee, state Treasurer Shannon O’Brien. He seemed to gain traction, though, with an attack ad that played up the losses that the state’s pension fund incurred on O’Brien’s watch from investments in Enron.

O’Brien countered by reviving the SCM story, running ads on the incident and calling Romney “the face of corporate greed in America.” She also launched an spot called “Sizzle” that featured a laid-off worker from GST – the same steel company Obama is now highlighting – who told viewers:

“It’s hard to believe that a man like Mitt Romney can have enough power and influence and money behind him to come in, destroy families, put people out of work that’s sick, with no health insurance. There’s nothing left. We have nothing left.”

O’Brien, though, lost to Romney by 7 points. This doesn’t mean the Bain attacks backfired. As Boston journalist Dan Kennedy noted today, Romney struggled throughout the ’02 general election more than the prior two GOP candidates – Paul Cellucci and Bill Weld – had. And it may have been a last-minute push by Romney to link O’Brien to unpopular Democratic leaders in the state Legislature that moved voters. Still, the fact remains that O’Brien played the Bain card aggressively, and it didn’t bring her to victory.

2008 Republican primaries: Bain was not a huge issue in this race, but when Mike Huckabee said that Romney reminds people of “the guy who laid you off,” he was clearly trying to harness the instinctively negative feelings that even many blue-collar Republicans have toward the world of venture capital. That line may have helped Huckabee in Iowa, where he beat Romney by 9 points.

Then, in the run-up to Florida’s primary, John McCain directly attacked Romney over Bain, arguing that “as head of his investment company he presided over the acquisition of companies that laid off thousands of workers.” McCain ended up winning Florida narrowly, a result that cemented him as the clear front-runner and dealt a severe blow to Romney’s hopes.

2012 Republican primaries: The attacks on Bain were far more pointed in Romney’s second bid for the GOP nomination, with Rick Perry accusing him of practicing “vulture capitalism” and Newt Gingrich branding him a “predatory corporate raider.” The Gingrich campaign even created a vicious 29-minute video titled “King of Bain,” which was released about a week before the South Carolina primary:

Democrats, of course, were delighted by this development, and an income gap came to define the GOP race, with Romney generally cleaning up with affluent Republicans voters but often losing to Gingrich (and later Rick Santorum) with those in the working and middle classes. At the same time, Gingrich took immense heat from leading Republican voices, who blasted him for doing dirty work for Democrats and defended Romney’s Bain work. And Santorum refused to join the Bain pile-on, saying that “I just don’t think as a conservative and someone who believes in business that we should be out there playing the games that the Democrats play, saying somehow capitalism is bad.”

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.