When Bob Brady finally announces his mayoral candidacy at the Convention Center tonight, it will end months of will-he-or-won't-he speculation about the congressman and longtime leader of the mighty, if moldy, Philadelphia Democratic machine.

But the declaration by a man who until recently was more a fence-mender than a political striver will raise new questions, too:

Can Brady, who has never faced a tough election campaign - at least not as a candidate - take a punch?

Will his history of cross-racial appeal, forged representing a mostly black congressional district since 1998, withstand the polarizing climate of a Philadelphia mayoral race?

And will Brady also reap the benefits of his status as the best-known white candidate facing three formidable African Americans in a city that traditionally votes along racial lines?

The most important question, though, is whether the venerable political organization that Brady, 61, has ruled since 1986 is still strong enough to put one of its own in City Hall.

The answer will likely determine whether Brady is rewarded with the keys to Room 215 of City Hall after 20 years of doling out the City Democratic Committee's patronage jobs, endorsements, and political cash.

"This will be a real test," said Carl Singley, a lawyer and city political veteran who is supporting one of Brady's rivals, State Rep. Dwight Evans. "Brady claims he's got all these chits of people that he got jobs for that he can call in. Well, I think he's in for a rude awakening."

Brady's supporters say such criticisms miss the point. Brady's deal-making, said City Councilman Jim Kenney, is a management style that could help him lead the city - not just a way to win elections.

"His biggest skill is the ability to get different people, sometimes warring factions, rowing boats in the same direction," Kenney said of Brady, whose formal education ended with a high school diploma. "That's what politics is. You could be a Harvard graduate and not get people to see things your way, and what good are you? He's done it."

Kenney will be among dozens of elected officials on hand at tonight's kick-off event - City Council members, row officers, and judges, the regulars of the local Democratic establishment (and, conveniently for Brady, people who happen to need the party's endorsement when they, too, face the electorate in May).

Kenney was mindful, though, that the collection of Democratic insiders alone wouldn't be able to swing the election.

"Me being there doesn't get him one other vote," he said. "You can get someone to change their opinion on [a race for] judge, but mayor? Uh-uh."

Brady has declined to comment since announcing his forthcoming announcement on Monday. But his speech at a December fund-raiser offered an indication of what a campaign might sound like.

After acknowledging a host of local political heavyweights in attendance, Brady, who grew up in West Philadelphia, launched into a nostalgic evocation of the rowhouse city of his youth - a place where parents could walk their kids to school in safety before heading off to decent-paying jobs. And, it went without saying, a place where ward leaders pulled in votes for the party boss.

"Affordable housing . . . a safe street, a decent education - that's the neighborhood I know," he said. "Everything else is secondary." Accomplishing all this, he added, was "nothing hard - it's pitching in together."

In this year's field of candidates, that sentimental tone may serve to set Brady apart from his rivals.

While businessman Tom Knox touts his outsider credentials, former Councilman Michael A. Nutter has proposed radical changes to the city's tax and ethics laws, and U.S. Rep. Chaka Fattah first gained office by defeating pillars of the party establishment, Brady is positioned as the champion of those who don't rock the boat.

So far, it has worked well, at least in the all-important test of political fund-raising. Last month, he signed off on the creation of a political action committee named "Friends of Bob Brady," and his campaign aides have said the committee has close to $1 million in the bank already. Details of his campaign's finances are due to be made public Wednesday.

And, in a sign that Brady will be seeking votes where some white politicians don't, he has already met at least twice with the Black Clergy of Philadelphia and Vicinity - hoping, like his rivals, to win the endorsement of the influential group, which includes ministers from more than 400 Philadelphia churches.

If the campaign he launches tonight ends in failure, Brady may find his status in the local political firmament at risk. Rivals have already threatened challenges to his congressional seat - something that would have been unthinkable a few months ago. A defeat in the May 15 mayoral primary could invite more aggressive challengers.

"Nobody has ever gotten rich betting against Bob," said political consultant Larry Ceisler. "But this is different. Now he's out there having to talk about issues. Instead of being the person behind the scenes and at the table, he's now the person onstage."

Contact staff writer Michael Currie Schaffer at 215-854-4565 or mcschaffer@phillynews.com.

Inquirer staff writer Marcia Gelbart contributed to this article.