Rudy Giuliani's downfall in the Republican primary fight has been much predicted, but little in evidence. He just got the endorsement of the Christian conservative leader Pat Robertson and has stubbornly stayed atop national polls all year long.

His success has spawned theories about the changing nature of the Republican Party, and how social conservatives have "grown up" in their willingness to accept a pro-choice candidate. The key to Rudy's appeal, though, isn't his heterodoxy, but how the sensibility of his candidacy is in the Republican mainstream running from Ronald Reagan through George W. Bush.

Rather than a break with Bush, Giuliani represents stylistic continuity. The cross-dressing, nonchurch-going, pro-choice New Yorker has more in common with the brush-clearing, evangelical, pro-life West Texan than any of the other Republican candidates. He's an urban cowboy, who tamed New York City with his no-nonsense commitment to law and order.

As a top GOP operative says: "Reagan has provided the stylistic model for Republican leaders ever since he first ran: tough-talking, moral clarity, inspirational rather than tactical in rhetoric, someone who will stand up to dangerous foreign enemies. Bush fits in that model, and so does Rudy. This style and these attributes are as important, if not more important, than particular issue stands to many voters."

At this basic level, Giuliani tugs on Republican heartstrings. There is no substitute in politics for being liked, and Republicans simply like Rudy. Rather than the abrasive personality they were told to expect, voters have seen a candidate with the readiest toothy grin this side of Jimmy Carter or Teddy Roosevelt, and he's the only Republican who has consistently demonstrated a spontaneous sense of humor.

In the breadbasket of modern Republicanism, the South, Giuliani has been surprisingly strong. The South is as much a state of mind as a geographic location, and Giuliani, despite being an ethnic Northeasterner, exemplifies it. He taps into the South's anti-elitist, patriotic, pro-military attitudes more naturally than any candidate besides John McCain.

Giuliani is winning the leadership primary in the Republican race. An October Fox News poll asked whether Giuliani is a "strong and decisive leader"; 65 percent said "yes," 20 percent "no" -- the highest rating of any of the tested national figures. By refusing to check the box on every conservative issue, Giuliani has reinforced the idea that he has exactly the attributes of strength and leadership that conservatives crave.

All that said, a similarity to President Bush won't be an asset in a general election. Bush was ill-served by his excessive loyalty to a tight, hermetically sealed group of advisers, and didn't take criticism well. Giuliani has the same tendencies. He gives the impression of being even less interested in diplomacy than the Bush of the first term. The change voters are looking for probably isn't "Bush -- except even more bellicose and disdainful of political opponents."

Giuliani still has major ideological -- and personal -- vulnerabilities. The question is whether the liberal aspects of his record as mayor, together with his spectacularly rocky personal life, will overwhelm his instinctual appeal to Republican voters. We won't know until we see how he fares under what probably will be a barrage of negative ads in the stretch-run of the nomination fight.

He likes to say that a winning Republican coalition consists of economic conservatives and national-security hawks -- pointedly excluding social conservatives. As a factual matter, this is wrong; Republicans can't win national elections without appealing to social-conservative voters who might not buy their free-market economics. As a tactical matter, it's foolish; he should continue to minimize his differences with social conservatives rather than implicitly read them out of the GOP coalition.

Giuliani's best selling point in the primaries is that -- whatever his media coverage says -- he's not something new under the sun. He's an archetype that Republican voters know and love -- the gun-slinging sheriff, just with a different ZIP code.