The Republicans have lucked out. They appear poised to nominate a guy who can actually win the presidential election in November - a possibility few Republicans had seemed willing to entertain, given the heavy baggage of George W. Bush.

And yet, party conservatives seem apoplectic about John McCain's surprising rise. Shrugging off his electability, they are fixated on his ideological impurity. For all their professed fealty to Ronald Reagan - a name invoked so often it has been shortened to Runnarigin - they are willfully violating the Runnarigin Rule, which holds that "the person who agrees with you 80 percent of the time is a friend and ally."

The purity enforcers don't realize how good they have it. Barring a near-miraculous late surge by Mitt Romney, the party will wind up tapping a hawkish career conservative who has pull with independent swing voters. Nobody else can do that, especially not this year. Nobody else has the heroic life story. Nobody else has the chops to beat Hillary Rodham Clinton - who, Obamamania notwithstanding, is still the most likely autumn finalist for the Dems.

McCain is the scourge of the conservative base, the butt of incessant insults. Rush Limbaugh warns that McCain as nominee would "destroy the Republican Party." Hugh Hewitt, another talk-radio luminary, says that a McCain victory would signal "the surrender of the party of Reagan." Rick Santorum warns that McCain would be "very, very dangerous." Tom DeLay complains McCain "has done more to hurt the Republican Party than any elected official I know of," quite a charge from a former House leader under indictment for alleged money-laundering.

Paul Mirengoff, a prominent blogger, says that a McCain presidency would be "four years of watching him stick it to conservatives." Michelle Malkin says McCain's modus operandi is to "insult the base, trash the base, and pay lip service to the base only when it suits his needs." Others even liken McCain to Bob Dole, another senior Republican war hero, whose indifference to the purists helped fuel his 1996 election defeat.

Granted, they're incensed by McCain's ideological heresies (his acceptance of global warming, his opposition to waterboarding, his opposition to a gay marriage ban in the Constitution, his attempts to curb the influence of money in politics, his early opposition to the Bush tax cuts).

But I also suspect they're simply stunned he's vertical at all, since he was pronounced horizontal just six months ago, when top staffers quit and the money dried up. Hence their cries of anguish. They did not imagine he could possibly surge to the fore, catching every possible break along the way.

Consider: Mike Huckabee (Baptist pastor and evangelical favorite) upset Romney in Iowa, softening up Mitt for a McCain victory in New Hampshire. Eleven days later, Fred Thompson (the purported conservative savior who barely registered a pulse) split the religious-right vote with Huckabee in South Carolina, allowing McCain to eke out a victory. Earlier this week, Huckabee split the religious-right vote with Romney in Florida, allowing McCain to win again. Huckabee will probably do McCain a similar favor in the multistate marathon this Tuesday, by splitting core conservatives with Romney. And, lest we forget, Rudy Giuliani's precipitous flameout has now left McCain as the favored candidate of national-security hawks.

As a result - and this is what surely galls the critics - McCain has scrambled to the top of the heap without help from the right-leaning true believers. They have not vetted him, and still he ascends. His early primary victories were powered by the votes of independents and crossover Democrats. And last Tuesday in Florida, while other candidates were splitting the hard-core conservatives, McCain was the overwhelming choice of moderate Republicans, Hispanic Republicans, Republicans who want to keep abortion legal, Republicans who favor a path to citizenship for illegal aliens, and Republicans who dislike the Bush administration.

But if McCain's critics think pragmatically, they will realize that the results thus far demonstrate why McCain could be formidable in November. Put simply, elections are won in the middle of the electorate. McCain has clout in the middle, where independent swing voters predominate. He is, in fact, more popular among independents than Hillary, as polls have long indicated.

One might ask how McCain could be strong with swing voters, since his hawkish stance on the Iraq war is out of sync with their antiwar sentiment. And yet he is - classic evidence that personality trumps the issues. In New Hampshire last month, independents repeatedly said they were torn between voting in the Democratic primary for Barack Obama (antiwar) or in the GOP primary for McCain (pro-war). They perceived McCain as an authentic person, therefore likable and worthy of trust.

So here's the nightmare scenario for Democrats: Hillary and McCain square off. McCain wins the independents, many of whom are sick to death of the Clintons. McCain cancels out Hillary's "experience" argument, because he has more. McCain trumps her "toughness" argument, because he has the more hawkish pedigree and spent five years in a POW cell. McCain trumps her on "authenticity," for reasons already mentioned. McCain even pulls away Hispanic voters in key states, thanks to his early championing of a path to citizenship. And he's buoyed by a united conservative base, because nobody galvanizes the base better than Hillary.

Democrats, even with the wind at their backs, have been asking each other, "How are we going to manage to lose this time?" Barring Obama's nomination, the scenario above is how. But it won't happen unless the conservatives park their grievances and unite behind McCain. As the old saying goes, even when Republicans don't fall in love, they win by falling in line.