So why is Rudy Giuliani — a thrice-married, pro-choice, Italian Catholic from New York — the leading candidate in a party that has moved steadily to the South, the West and the Right?

The main answer is Hillary Clinton. So many Republicans are so petrified of a new Clinton epic (The Comeback Kid 2) that they’re ready to bite their tongues, hold their noses and swallow their pride if Rudy has a chance to win. As Mike Huckabee summed up the GOP mood: “There’s nothing funny about Hillary being president.”

But that’s not the whole story. Giuliani is running a skillful campaign, reframing the issues facing Republican voters to focus on his strengths (terrorism and crime) while diminishing his weaknesses (abortion, guns and gays). And here, Hillary provides another foil.

She’s a sitting senator, and has never even run a “corner store,” as Mitt Romney puts it; Rudy has run one of the nation’s biggest cities, and Americans much prefer leaders with executive experience. That’s why four of our last five presidents have been governors.

Of course, Americans have a love/hate relationship with New York, attracted by the glitz and repelled by the sin, and Giuliani is exploiting that ambivalence, running as mayor of “Gomorrah on the Hudson” and boasting about all the criminals, vagrants and pornographers he swept off the streets.

But a lot of that was before 9/11. Since then, New Yorkers have become heroes, figures of virtue not vice. Ground Zero is sacred territory and the world is a dangerous place. Republicans hate Hillary but they also hate Osama and Saddam, and 45 percent of them prefer Rudy to handle the terrorism issue. John McCain lags 18 points behind on that question, Romney barely registers.

Moreover, Rudy has decided to speak frankly about his differences with the religious right, hoping to get credit for candor and consistency. He wants his bus to be this year’s version of the Straight Talk Express. As he told a meeting of “values voters” last weekend: “Isn’t it better that I tell you what I really believe instead of pretending to change all of my positions to fit the prevailing wind?”

He’s even confessing his past sins, to the public if not a priest, telling that meeting: “You and I know that I am not a perfect person.” His past wives and current children would certainly agree with that statement, but it has a political purpose beyond personal atonement.

Americans love stories of redemption and resurrection, and Giuliani was aiming at that target when he said, “I pray for forgiveness.” Remember, the current president was an alcoholic until he found God and Laura, the two forces that saved his life and career.

Rudy still has plenty of enemies in the GOP. In a straw poll at the “values voters” meeting he finished a miserable eighth. Some religious conservatives insist they won’t vote for him if he wins the nomination. But he has surprised almost everyone by maintaining his lead in national polls only 10 weeks before the Iowa caucuses.

In the latest Washington Post/ABC survey he runs 17 points ahead of the second-place finisher, Fred Thompson. In a review of recent polls by the Web site Real Clear Politics, his average lead is 9.2 percent. And the biggest chunk of that advantage is based on a simple, four-word slogan: “I can beat Hillary.”

Half of all GOP voters say he has the best chance of winning. No other candidate scores above 15 percent on that question, which shows that even deep-dyed conservatives recognize reality. No one can win the presidency just by appealing to a base vote. Reagan, every Republican’s hero, made deep inroads with “Reagan Democrats,” many of them ethnic Catholics like Giuliani. Bush 43 peeled off centrists by making a promise that he never kept, to govern as a “compassionate conservative.”

Of all the Republicans running this year, Giuliani has the best chance of duplicating that political feat. “I’m the one who can be a coast-to-coast candidate,” he says, and he’s right. But it’s the fear of Clinton that gives his argument extra weight.

She has replaced Sen. Ted Kennedy as “the Great Satan” of Republican mythology. Almost every GOP candidate at the party’s debate last Sunday invoked her name, and that tactic actually helps Giuliani. The more she’s mentioned, the greater the anxiety; the greater the anxiety, the better Rudy looks.

From a political standpoint, Hillary is Rudy’s new best friend. He can’t win the nomination without her.