Tonight’s runoff in North Carolina’s 8th district features arguably the most contentious insider-versus-outsider House fight of the campaign to date. And the race says a lot about how the Republican party establishment has evolved in its effort to beat back tea party challenges.

Two years ago, dentist Scott Keadle would have been a favorite to beat former congressional aide Richard Hudson in tonight’s runoff for the right to face Rep. Larry Kissell (D-N.C.). Keadle, after all, has the Club for Growth behind him, and Hudson is easily tied to an unpopular Washington.

Today, the tea party enthusiasm that swept people like Keadle into office (and past establishment favorites like Hudson in the primaries) has dissipated considerably.

But almost equally as important as that decline in tea party enthusiasm is that outside groups have stepped up to help establishment candidates like Hudson effectively muddy the waters on who is the “conservative” and “outsider” in these primaries.

In North Carolina’s 8th district, the American Action Network and Young Guns Action Fund — two establishment-oriented outside groups more concerned with keeping the GOP in power than electing strict conservatives — have outspent the Club for Growth.

AAN and YG Action Fund have spent $761,000 over the last three weeks for Hudson, while the Club for Growth spent just more than $400,000 on Keadle’s behalf.

The Club is no longer on the air in the district, which analysts say suggests the race may be a lost cause for them and Keadle (though runoffs are notorious for surprises due to the likelihood of low turnout).

“With the Club for Growth’s support of Keadle, that muddied the waters a bit in terms of the runoff outcome,” said North Carolina political analyst Jonathan Kappler. “I think others that wanted Hudson to win thought the same thing, which is why I think the YG Action Fund and the American Action Network came in for Hudson with pretty big ad buys (plus mailers). In my mind, this additional spending to benefit Hudson has helped tip things back in his favor, and I give him an edge today.”

Whether or not Hudson wins, though, the strategy of his campaign and his supporters is notable.

While in the past, establishment-backed candidates struggled to beat back outsider candidates with little or no record to attack (and many times were simply caught off-guard by the seriousness of tea party challenges), these groups have now found a blueprint with which to fight back.

AAN has run an ad tying Keadle to President Obama’s stimulus package, noting that Keadle, as a county commissioner, voted to accept stimulus funds. Hudson, meanwhile, has worked to shore up his right flank, winning a tea party straw poll last week and securing the endorsements of conservative favorites Mike Huckabee and Rick Santorum.

Suddenly, this race isn’t so clearly a tea party outsider versus the establishment.

Club for Growth spokesman Barney Keller disagreed with that characterization, arguing that outside spending on Hudson’s behalf has only reinforced him as the establishment candidate.

“Eric Cantor and the Young Guns’ actions in the race in North Carolina are just further evidence that the Republican leadership is more interested in protecting their insider friends and cronies than advancing conservative policies and ideas,” Keller said. “I thought it was impossible for grassroots conservatives to be more skeptical of the Republican leadership, but (House Majority Leader) Eric Cantor’s Young Guns may soon test that thesis.”

YG Action Fund spokesman Brad Dayspring responded: “This is about winning, and electing conservative candidates like Richard Hudson who are emblematic of the Young Guns movement is an essential step toward going on offense to protect and expand the majority.”

It’s a dynamic we’ve seen play out in other races too. In Utah, Sen. Orrin Hatch (R-Utah) beat back a conservative primary challenge by relentlessly courting them for the better part of the last year. His supporters also successfully made an issue of Freedomworks, the outside group backing former state senator Dan Liljenquist. By the end of the race, FreedomWorks was a four-letter word and Hatch won easily.

Similarly, in the increasingly contentious Wisconsin Senate primary, nobody is letting businessman Eric Hovde run away with the outsider label. Though Hovde is the only candidate in the race that hasn’t held elective office, his opponents have worked hard to label him a Washington insider (having been in the nation’s capital for decades), and supporter of higher taxes, the stimulus and bailouts.

Outsider — and tea party-aligned — candidates, of course, are still winning races. (See Richard Mourdock in Indiana.) But the establishment hasn’t taken as big a drubbing this primary season as it did two years ago.

Back then, candidates like Hovde, Liljenquist and Keadle might have been disregarded early on and allowed to gain momentum. These days, nobody is underestimating the chances of an outsider, and they are responding accordingly.