At a time when conservative populism is the political gospel of the GOP establishment, Mayor Bloomberg has increased his lead for re-election by quietly reviving a political tradition long thought dead: the Rockefeller Republican.

Stratospherically wealthy and socially liberal, Bloomberg resembles the former three-term New York Governor Nelson Rockefeller far more than the mayor resembles his immediate City Hall predecessor, Rudolph Giuliani. The harder edges are softened, political hopes are pinned not on crime reduction or welfare reform but on education policies and outreach to minority communities that often comes with a government or personal check attached. When the Republican Convention came to town, Mr Bloomberg advocated for a more inclusive GOP pointedly attending events for pro-choice and gay Republicans while declining to be photographed with President Bush. Traditional social and fiscal conservatives may complain, but there is fresh evidence that his Rockefeller Republicanism is beginning to sway local voters across ethnic and party lines. Still, some professional consultants remain concerned that Bloomberg’s support is “a mile wide but an inch deep” and that that could spell trouble in New York City’s fall mayoral election.

First, the good news: Even after a bruising month in which Mr. Bloomberg saw his West Side stadium dreams suddenly collapse, the new Quinnipiac poll shows good news for the mayor. He now decisively leads all his Democratic opponents, and his overall job approval rating has finally passed the 50% mark. In March he was losing to the front-running Democratic candidate, Fernando Ferrer, by 47% to 39%. He now leads Mr. Ferrer, 50% to 37%.

Most heartening and startling for a Republican is Mr. Bloomberg’s surprisingly strong support from minority communities. The poll shows him with 40% support from both the African American and Hispanic voters in a head-to head race against Mr. Ferrer, the first serious Hispanic candidate for mayor in a generation. This level of minority support is among the highest for any Republican in the nation, a throwback to the misty liberal Republican days of Rockefeller and Mayor John Lindsay.

There is however, credible concern that Mr Bloomberg’s strong summer support could evaporate amid the hard political realities of the fall. While the mayor’s support among African-Americans and Hispanics is a strong endorsement of his conciliatory approach to the office, New York City politics has traditionally been defined in the angling between competing minority groups. It is unlikely that Mr Bloomberg will be able to hold on to his high levels of voter support among these traditionally yellow dog Democratic groups.

Here is where the numbers get rough for the incumbent mayor. Republicans in 5-to-1 Democratic New York have very little margin for error: They must ensure nearly 100% turnout of their base while also effectively reaching out to other voters. In 1997, Mayor Giuliani cruised to a re-election victory over West Side liberal fixture Ruth Messinger, winning four out of the city’s five boroughs. Mr. Giuliani claimed support from 45% of Democrats, 65% of independents as well as 92% of Republicans. He captured nearly half of Hispanic male voters and 40% of gay and lesbian voters, but Mr. Giuliani was also embraced by many conservatives, and his campaign inspired strong turnout in the more blue-collar conservative outer boroughs.

It is difficult to imagine Mr. Bloomberg winning Brooklyn as decisively as Mr. Giuliani did despite the shifting demographics and improved quality of life, which should benefit the moderate Republican. Likewise, the battleground borough of Queens is very much in play, and the idea that Mr. Bloomberg might win the borough 64% to 33%, as Mr. Giuliani did, seems to be a dream.

Moreover, the one candidate Mr. Bloomberg loses to in the current Quinnipiac poll is an unnamed Democratic primary winner, suggesting that many Democrats who are more or less happy with Mr. Bloomberg’s tenure as mayor might not stick with him when push comes to shove in the fall election. This lack of loyalty to the Mayor Bloomberg brand is further highlighted by concerns about low Republican voter turnout and the possibility that the protest candidacy of former City Council Republican leader, Thomas Ognibene, could siphon off crucial support if Mr. Ognibene receives the Conservative Party ballot line in the fall. As one statewide Republican consultant who asked to remain unnamed told me, “If Ognibene can get just 3% on the Conservative Party line, Bloomberg cannot mathematically win, as every single one of those Ognibene voters comes from the Republican line.”

The X factor in this year’s mayoral race is Mr Bloomberg’s unprecedented potential for self-funding, a practice that was practically pioneered by Nelson Rockefeller. It is difficult to quantify the precise effect that $100 million can have on a tight race, but in the case of Rockefeller there was a saturation point at which his self-funding ads began to turn off some swing voters in his 1964 bid to run for president. Mr. Bloomberg does not appear to harbor any such national ambitions; he has not attempted to establish himself as a national spokesman for a more moderate urban brand of Republicanism. But if he wins re-election and Governor Pataki either leaves or loses office to a Democratic contender – as seems increasingly likely – Mr. Bloomberg would be come the state’s leading Republican. What he would choose to do with that bully pulpit might help to redefine the state party and the legacy of Rockefeller Republicanism.