WASHINGTON — Republicans are now left with only one question: Can anyone stop John McCain?
The Arizona senator swept big state primaries Tuesday, grabbing hundreds of delegates and a huge lead in the tally needed to secure the Republican presidential nomination on the first ballot at the convention in St. Paul, Minn.
With 47 percent of the convention delegates still up for grabs, it's still mathematically possible for one of McCain's two top challengers to win. It's just much, much harder for them after McCain's Super Tuesday victories.
McCain now has a big lead, with 613 of the 1,191 delegates needed to win the nomination, according to the Associated Press' count.
Former Massachusetts Gov. Mitt Romney has 269, and former Arkansas Gov. Mike Huckabee has 190.
That means McCain has to win roughly 45 percent of the delegates that are still up for grabs — not even half — to secure the nomination. He actually could lose states and still win the title, particularly since many coming contests will award delegates even to second-place finishers.
Romney, however, has to capture 73 percent, and Huckabee 79 percent, to win. Those are much steeper climbs.
Also, the conservatives who despise McCain appear unable to coalesce behind either Romney or Huckabee, and Tuesday's results exacerbated their problem.
McCain's weakness — and the opening for a challenger — is that he still hasn't locked up the party's conservative base.
Despite McCain's strong stand on defense, many conservatives consider him a closet liberal, hostile to tax cuts, supportive of illegal immigrants and too ready to compromise with the likes of Sen. Edward Kennedy, D-Mass.
Some conservative voices, such as talk show host and Fox News personality Sean Hannity, are rallying to Romney as the best alternative to stop McCain.
Romney has one great strength that Huckabee lacks: money. He's raised tens of millions more than Huckabee, and when he's needed even more money to buy TV ads in an expensive market such as Florida or California, he's reached into his deep pockets and lent his own cash to the campaign.
But others who blast McCain haven't warmed to Romney because they consider him either an unconvincing convert to their causes — he once supported abortion rights and gay rights — or a loser who couldn't win in Iowa or New Hampshire despite herculean efforts.
Romney likely further hurt his claim to be the anti-McCain by a weaker-than-expected showing Tuesday in states such as California, Georgia and Missouri, where he thought he had a good chance.
James Dobson, the influential social conservative who heads the Colorado-based group Focus on the Family, said Tuesday that he wouldn't vote for McCain — but he stopped short of backing Romney.
"I am convinced Senator McCain is not a conservative, and in fact, has gone out of his way to stick his thumb in the eyes of those who are," Dobson said. "I cannot, and I will not vote for Senator John McCain, as a matter of conscience."
Huckabee, on the other hand, has had a hard time broadening his base beyond social conservatives.
He's also run afoul of some movement conservatives, in part because he raised taxes as governor. Talk-radio host Rush Limbaugh, for example, lumps Huckabee and McCain together, saying either one would drive angry conservatives to sit out the fall election and essentially destroy the Republican Party.
All of which leaves McCain in the driver's seat — of a car with wobbly wheels on its right side.