On the eve of the Super Tuesday primaries that would confirm him as the front-runner for the Republican presidential nomination, John McCain joined two heretical members of a party that has made itself synonymous with orthodox conservatism–California Governor Arnold Schwarzenegger and former New York Mayor Rudy Giuliani, both supporters of abortion rights, gay rights and reasonably functional government–at a solar technology plant in Los Angeles. They talked about their shared commitment to address global warming. And they reminded everyone that the Republican Party of John McCain is not the Republican Party of George W. Bush or Rush Limbaugh.

While Democrat Barack Obama’s remarkable challenge to Hillary Clinton and the Democratic establishment may yet be the essential story of 2008, McCain’s march toward the Republican nomination is the year’s more improbable journey. Since climbing out of the campaign coffin to which he was consigned last summer when his fundraising fell short, McCain has elbowed his way to the front of the Republican pack with a “coalition” that does not rely on the people who thought they ran the party, winning primary after primary with the votes of independents and self-identified GOP moderates, while the right has divided between country club conservative Mitt Romney and evangelical populist Mike Huckabee. Romney and Huckabee both promise to soldier on, but the former governor of Massachusetts is now widely perceived as having blown a personal fortune on a campaign that was overshadowed on Super Tuesday by the live-off-the-land campaign of the former governor of Arkansas. But Huckabee’s win came with a footnote: although he prevailed in his native South, he was barely in the running elsewhere. He’s still got Mississippi, but after that he’s going to run out of states of the old Confederacy. On most maps, McCain looks inevitable.

That prospect enrages the celebrity conservatives, who thought the Grand Old Party was their affair. As the more theatrically than really maverick senator from Arizona began closing in on the nomination, Romney labeled McCain a “liberal” while radio ranter Limbaugh predicted a McCain win would “destroy the Republican Party.” Cuckoo-con Ann Coulter said she would campaign for Hillary Clinton over John McCain, a declaration roughly equivalent to the Pope backing Beelzebub over a dissenting Jesuit. Are right-wingers crazy? What could they possibly find troubling about a self-declared “foot soldier in the Reagan revolution” who was the key campaigner for Bush’s re-election?

The answer has more to do with that trip to the solar plant in LA than with the particulars of a lifetime American Conservative Union rating of 82 percent, which ought to make McCain entirely acceptable to the right. What distinguishes the senator from other prominent Republicans is what horrifies the party’s right flank and makes him the GOP’s most viable November contender: McCain tends to accept the idea that there is a mainstream that extends beyond the Fox News Channel’s viewership. To a party that has placed a premium on extreme purity–and to commentators who make their money enforcing ideological standards–McCain seems unsettlingly inclusive. He refers to the GOP as “a big-tent party” and signals that he is more interested in filling that tent than in joining the conservative commissars who guard the gate. Asked about Limbaugh’s criticisms, this regular Letterman guest replied, “I don’t listen to him. There’s a certain trace of masochism in my family, but not that deep.”

The Limbaughs, the Coulters, the editors of Human Events and the Wall Street Journal, the tanked thinkers of the Heritage Foundation and the myriad defenders of the right-wing franchise are not used to such disrespect, and they have responded with vitriol so intense that The Weekly Standard, which shares McCain’s obsession with less jobs/more war policies, refers to the right’s “McCain derangement syndrome.” It’s not an entirely irrational hatred, however. The professional conservatives are losing a fight for their party. Not since Gerald Ford narrowly beat Ronald Reagan for the GOP nod in 1976 has anyone gotten close to being nominated without bowing and scraping at the altar of social, economic and military-industrial conservatism designed by the high priests of the rigid right. Over time, the GOP’s range of debate has narrowed so much that Barry Goldwater is now viewed as suspiciously liberal.

The Bush/Cheney years have been characterized by an unapologetic embrace of unyielding right-wing dogmas. Even if they did not govern with the consistency that their rhetoric suggested, the Administration and a pliant Republican Congress did their best to mainstream extremist notions. Along the way, they winked and nodded as a Republican Taliban pursued the ideological cleansing of the party. Senior Republicans deemed guilty of even minor deviations from conservative dictates were denied Congressional committee assignments, dismissed as liberal traitors, booed at state party conventions and even “primaried”–as were Pennsylvania Senator Arlen Specter, who narrowly survived, and Michigan Representative Joe Schwarz, who didn’t.

No “Republican in Name Only” has been more consistently distrusted by professional conservatives than McCain. He was too popular in Arizona to challenge in a GOP primary–even if the state’s conservative mandarins have campaigned against him this year–and too useful to Republicans in tight races, including Bush in 2004, to push aside completely. But for most of the Bush/Cheney era, McCain has been the definitional RINO, and conservative commentators have memorized his litany of sins: a partnership with liberal Democrat Russ Feingold to promote campaign finance reforms that constrained the gaming of the political process by corporate interests, a brothers-in-arms relationship with fellow Vietnam vet John Kerry, tax-the-rich votes, frequent fights with evangelicals who don’t get his sense of humor but intuit that he’s laughing at them rather than with them, off-message criticisms of torture, an alliance with liberal icon Ted Kennedy to promote immigration reform–and that break with the Administration on climate change.

McCain is no moderate. His record on social and economic issues was to the right of Romney’s until recently, and the former POW’s determination to wage wars that give new meaning to the term “quagmire” is striking. He can rant about “Islamofascism” and America as “a Judeo-Christian nation” with the craziest of his conservative comrades. Yet McCain remains a card-carrying member of the centrist Republican Main Street Partnership, which promotes “principled and pragmatic” moderation in a Republican Party where them’s fightin’ words. “McCain is still viewed by the moderate wing of the party as a savior at this point,” notes political scientist Tom Schaller.

That would make his securing of the nomination–if and when he dispatches Romney and Huckabee, whose economic populism scares the “suicide voters” of the Limbaugh/Coulter faction more than McCain’s maverick nature–not the end but the beginning of the fight for the soul of the Republican Party. Fully aware that their influence is under threat, political and media conservatives will dog McCain. The fantasy of a third-party challenge from the right will be floated. How McCain responds will be the critical question of the spring and summer. If he starts listening to Limbaugh, his campaign will not be “the end of the Reagan era” that conservatives bemoan but a continuation of the Bush era–and his candidacy will be easily characterized by Democrats as the antithesis of change.

On the other hand, if McCain assumes he will ultimately retain the support of the right–with which he sides on most issues and for which he is the only alternative to an Obama or Clinton presidency–the senator can position his campaign as a break with Bush and, potentially, forge a Republican Party that is more concerned with winning elections than perfecting its ideological pedigree. That’s what professional conservatives fear, as they know their influence over such a party would be diminished. But it is, as well, what Democrats must fear. While a more moderate Republican Party might open up the process enough to give meaning to the word “bipartisan” and finally move some old dogmas–like denial of climate change–to the fringe, it might also be viable. The Republican Party as defined by George W. Bush and Rush Limbaugh does not stand a chance in 2008. Democrats may be enjoying that party’s knives-out fight with McCain now, but they would be wise to hope that McCain makes his peace with the pros and runs as their candidate. A maverick McCain, portrayed however falsely as something other than a conservative, really is the best hope of a Republican Party that may not like the occasionally heretical senator but that cannot possibly win without him.