As recently as last year, Pat Toomey was the face of the Republican civil war. In 2004, he was the Tea Party candidate before the Tea Party even existed, with his primary campaign against Arlen Specter prompting the Republican establishment from President Bush down to close ranks behind the incumbent and narrowly rescue him from defeat, warning of electoral disaster if Toomey were the nominee. After Specter ditched the party in 2009 in the face of a second primary challenge, Toomey once again became a lightning rod for Republican critics, who warned that the party couldn’t possibly prosper with ultra-conservative candidates taking out popular centrists in swing states like Pennsylvania.

Arguments about the direction of the GOP and the role of the new Tea Party movement have only intensified since then, but few of them now seem to center on Toomey, who is quietly proving his critics wrong with a dominant Senate run. In his place, a slate of Tea Party candidates who won their nominations with the model Toomey pioneered, including Sharron Angle in Nevada, Rand Paul in Kentucky, Christine O’Donnell in Delaware, and Joe Miller in Alaska, are soaking up national attention with their unconventional campaigns.

That Toomey is now treated as just another Republican candidate in the press has left longtime political observers on the right and left alike in a state of shock. David Bossie, president of Citizens United, told The Daily Beast that Toomey’s absence from most discussions of Tea Party candidates demonstrates just how far the conservative movement has come in the last two years.

“When Pat Toomey is a guy who’s considered pretty mainstream in that crew, that’s an amazing statement because he’s a phenomenal conservative leader,” Bossie said. “When we have this entire conversation and don’t even mention him, that’s unbelievable.”

Progressive blogger Josh Marshall recently threw his virtual hands up in amazement as well, crediting the other Tea Party candidates with making Toomey appear mainstream in comparison.

“He seemed close to unelectable in Pennsylvania,” the Talking Points Memo founder wrote in a post this week. “But up against Angle, Miller, O’Donnell, he’s like Bob Dole.”

After starting the general-election campaign even or behind Democratic Rep. Joe Sestak in most surveys, Toomey has steadily built a solid average lead of 6.6 points in the polls, according to Real Clear Politics, leaving his opponent scrambling to remind voters of the old conventional wisdom that Toomey is too extreme for Pennsylvania. The Sestak campaign—which dispatched Specter in the primary—recently rolled out ads linking Toomey to Sarah Palin and former Pennsylvania Senator Rick Santorum, who backed Specter in 2004 and was voted out in a landslide in 2006 after comparing gay marriage to bestiality. The campaign also has run ads attacking Toomey for his work as a Wall Street trader, portraying him as a free-market fundamentalist. There’s plenty of material for the Sestak team to work with—Toomey’s voting record in Congress is more conservative than that of Santorum, Senate Tea Party cheerleader Jim DeMint, and John McCain’s defeated primary challenger J.D. Hayworth, according to one pollster’s analysis. A Toomey spokeswoman told The Daily Beast that “if anyone is extreme, it’s Sestak,” citing his support for Democrats’ health-care and energy legislation.

Sestak is scrambling to remind voters of the old conventional wisdom that Toomey is too extreme for Pennsylvania.

• Kirsten Powers: What Do Dems Have Against Women?• Election Oracle: Predictions for the Hottest RacesFew of the attacks on Toomey seem to be sticking, however, in no small part thanks to a campaign that has been as conservative in demeanor as its been on the issues. In striking contrast to his fellow insurgent candidates, Toomey has downplayed his role in the broader conservative grassroots movement and eschewed its fiery anti-Obama and anti-establishment rhetoric in favor of a much quieter run. While Rand Paul dubbed his primary win “a message from the Tea Party” in his combative victory speech, Toomey used his to dub Republicans a “unified party all across the Commonwealth.” Even some Democrats grudgingly acknowledge the difference in perception between Toomey and his Tea Party descendants.

“I think he’s done a better job than some of the candidates of masking his true views,” said Jim Burn, chairman of the Pennsylvania Democratic Party, adding that one of the party’s top goals in the final stretch of the election is “to show voters Mr. Toomey is an out-there guy.”

While Toomey’s positions have not significantly changed since his 2004 run, he has made a careful effort to do some outreach to moderates as well, most notably in his support for Justice Sonia Sotomayor’s Supreme Court nomination last year.

Speaking to The Daily Beast for this article, Toomey spokeswoman Nachama Soloveichik was quick to name-drop several moderate Republicans who have held fundraisers for the campaign, including Susan Collins and Orrin Hatch. That would be the same Hatch who responded to Specter’s defection from the Republican Party by telling Politico, “I don’t think there is anybody in the world who believes he can get elected senator there.” Asked how Toomey fits in with other candidates who won anti-establishment primaries, Soloveichik downplayed any connection. “I wouldn’t compare him to anyone else,” she said.

“He’s no Christine O’Donnell or Sharron Angle—he comes across as reasonable, measured, he speaks in very precise terms and doesn’t sound like he’ll end Social Security as we know it or be a Wall Street puppet,” said G. Terry Madonna, a professor of public affairs at Franklin & Marshall College. “When you look at his voting record in Congress, he comes across as very, very conservative, but in this national environment it doesn’t have that same effect and he doesn’t sound like he’s off the charts.”

Toomey’s campaign may be proving to his many doubters that he can compete in a general election, but some detractors argue that the damage from his primary challenge is already done. Former Bush speechwriter David Frum, who wrote an influential piece slamming Republicans for pushing out Specter, said he stood by his critique, given that Specter ended up the 60th vote Democrats needed to pass health care.

“No Toomey, no Obamacare,” he said in an email. “My main point was not that Toomey was ‘too conservative’ but that his challenge to Specter over his stimulus vote achieved entirely counterproductive results from a conservative point of view.”

Benjamin Sarlin is the Washington correspondent for The Daily Beast and edits the site's politics blog, Beltway Beast. He previously covered New York City politics for The New York Sun and has worked for talkingpointsmemo.com.