Andrew Breitbart's fingerprints are all over the majority of the partisan political Internet. The Blaze, the Daily Caller, Huffington Post, even Politico: They'd all look quite different without his influence. There was already Rush Limbaugh and Roger Ailes and Matt Drudge himself, but Breitbart was a phenomenon of the Internet age, and would not have thrived before the Web helped to destabilize the traditional press.
He intuitively understood how the media work even if he needed to invent a grand conspiracy to explain the motivations of its primary actors. He knew that if the press felt it had missed a major story from an unexpected source, it would quickly rush to be the first to publicize further material from that source in the future. He learned this from Matt Drudge, who really did become the de facto "assignment editor" of the political press following his publication of Michael Isikoff's axed Lewinsky story. The parallel right-wing press has been in existence for years, and the early conservative blogosphere organized itself around blogs from people like Michelle Malkin and Glenn Reynolds, but Breitbart was an expert in forcing their obsessions into the "mainstream."
Before Breitbart mainstreamed conservative obsessions, he got a graduate-level course in how the MSM worked. Mickey Kaus, in his idealized obituary of Breitbart, tells the story that illuminates the power Breitbart had as the co-editor of the Drudge Report: Breitbart, working on a tip from Kaus, told the Smoking Gun to track down an old interview in which then-gubernatorial candidate Arnold Schwarzenegger bragged about participating in orgies. He publicized the result at Drudge, and it instantly became national news. Work at the Drudge Report was rarely quite so entrepreneurial -- usually news outlets would do the work on their own and beg for a link.
The end result of a media environment so fixated on the predilections of this one oddball and his hyperactive aide-de-camp was the rise of Drudge-baiting -- the pursuit and promotion of stories designed solely to attract the interest of the Drudge Report. This often involved freak weather and news about Madonna, but it mostly meant things that made Democrats look bad. (The Schwarzanegger story, chosen in part to illustrate Breitbart's essential fairness, qualified because it had just enough celebrity and sex to make up for the fact that it was damaging to a Republican.)
The sensibility was Drudge's, but Breitbart was the guy people in the press desperately befriended at parties. The new gold standard of long-form campaign reporting is Mark Halperin and John Heilemann's "Game Change," a book that tackles a presidential campaign as a series of hopefully Drudge-worthy nuggets of inane gossip. (Halperin's previous book was essentially an ode to Drudge's influence and import.)
The apotheosis of Drudge-bait is Politico, a site that aimed to take the national politics section of a newspaper and strip it of everything but Drudge-bait. Some days half its content seems to be relatively fact-free stories proposing or reinforcing Drudge-friendly narratives (Obama is angry and uses teleprompters, some say).
And there is the one-time "liberal Drudge," the Huffington Post, which now has consumed the content portion of AOL itself. Breitbart was a co-founder of the site, and though he wasn't there long, he made his mark. He loved the "celebrities blogging" gimmick that much of the early HuffPo was based around. This remains HuffPo's most mockable and often detestable feature. (One other idea he might've brought to the table: hosting slightly rewritten newspaper and wire copy on the site itself, instead of linking out, as Drudge did, to Breitbart's consternation.)
"Aggregators" like Drudge and HuffPo have mostly given way to partisan sites that specialize in the actual creation of content. Much of this content is designed as (unpaid) work-for-hire for larger news outlets -- be it Fox & Friends or MSNBC -- and Breitbart's "Big" sites helpfully designed and packaged ready-made pseudo-scandals for Fox and others to fixate on.
A fixation of the online conservative movement is "scalp-hunting": the elevation and demonization of some usually obscure liberal figure done in the hopes of getting them nationally shamed and fired. (Righties sort of do this as "retribution" for what happened to various conservatives who got in trouble and whose trouble was reported in the press, like Oliver North or Scooter Libby.) This is what the Shirley Sherrod video was supposed to be -- a routine Van Jones'ing -- and what it briefly was until it blew up in Breitbart's face. It can be done with dead people, like Saul Alinsky, and organizations, like the New Black Panther Party, though the firing of still-living individuals is the primary means by which the conservative press "keeps score," so it's best to narrow your focus.
The Sherrod video was also an example of the limits of another of Breitbart's gifts to modern media: the false "proof." It is a sad fact of online publishing that some ridiculous portion of readers only read the headlines and look at the pictures before moving on. (The percentage of online commenters who do this is approximately 90 percent, according to studies I have skimmed and had strong opinions about.) Breitbart's sites exploit this: "OBAMA MARCHES WITH NEW BLACK PANTHERS," or something like that, goes the headline. The story can't support the claim. It doesn't matter. The headline means it's true for the majority of the readership.
Shirley Sherrod's anti-white racism became a "fact" that led to her firing because of that convention of online muckraking. The headline said she was racist and there was a YouTube video attached that probably proved it, if anyone bothered to hit play and listen.
This is how right-wing myths are created and sustained -- did you hear that Oprah banned Sarah Palin from her show and Michelle Obama spent $30,000 on lingerie? Those are both lies, but they were also both Drudge headlines! -- and in a media environment where, thanks to the work of activist/publishers like Breitbart, most previously agreed-upon facts are regularly up for debate anew, introducing new myths can be full-time work.
And in his war on the "mainstream press," Breitbart played on a long-standing paranoia that Drudge's rise also depended on: a fear that all the "liberal bias" claims were in fact true, and that what seemed to be nutty, conspiratorial nonsense emanating from the right-wing fringe media was actually the next hot story.
(Breitbart used the standards of traditional "objective" journalism as a weapon, and it often helped his cause that he was simply too exhausting to argue with, unless you were particularly pigheaded.)
The most modern thing about Breitbart was that he was so ridiculous, and so extreme, and yet taken more or less completely seriously by the mainstream press he claimed to despise. (This is in part because he was fun at parties.) Screaming -- literally, screaming -- vulgar, stream-of-consciousness insults on national television used to be your ticket out of respectability with the news crowd, but now it is basically indulged.
Honestly, if he helped make false civility less of a requirement for being "taken seriously" in the media world, that is almost certainly a good thing. The rest of his influence is too tied up in the influence of the Internet itself on the world of information for him to be directly blamed, but he was the raging, filter-less, irresponsible, vitriol-spewing, tireless avatar of the new way of doing things.