With just over two weeks left until the Democratic mayoral primary, Britton Stewart's vote is still up for grabs.

"The candidates all seem to have a lot to offer," the 47-year-old social worker from West Oak Lane said. "I just don't have a favorite yet. I have a little time."

That should keep more than one campaign manager up at night.

Not that Stewart's ballot counts more than anyone else's. Rather, he is emblematic of other African American voters - who are expected to significantly influence the outcome of the May 19 primary - yet to decide whom to support.

How large a number that represents is hard to determine, but polling done on behalf of Jim Kenney suggests about 18 percent of all black voters remain undecided.

Why does that matter?

Well, an estimated 40 percent to 45 percent of registered Democrats are African American, representing the city's largest racial voting block. About 32 percent of registered Democrats list themselves as white.

If past election patterns hold true, a vast majority of those voters - white and black - will cast ballots along racial lines.

The last time the city chose a new mayor, in 2007, voters colored outside the lines: an African American, Michael Nutter, won a five-way Democratic race with strong white support despite having two well-known white candidates as rivals.

But those voters were an exception to the rule.

"I know we don't like to talk in this way, but the reality is there are still numbers of people in this city who vote along racial lines," said W. Wilson Goode Sr., the city's first black mayor, who benefited from nearly uniform black support when he first won in 1983. "I don't see that changing in this election in any significant way."

That fact provides the underpinning of the campaign of State Sen. Anthony Hardy Williams, the leading African American in the race. Williams' success turns on how large a percentage of the black vote he can secure, while denying Kenney and Lynne Abraham - the two other most competitive candidates at this point - as much of that vote as possible.

Kenney has aggressively worked to undercut Williams on his own turf. Last month, he scored a coup when he was endorsed by State Rep. Dwight Evans and City Councilwoman Marian Tasco, two of the city's most prominent black elected officials. City Council President Darrell L. Clarke was scheduled to offer his imprimatur Saturday by walking some North Philadelphia neighborhoods with Kenney.

There is a general consensus that Williams will need to attract at least 70 percent of the African American vote to have a chance of winning.

The only public polls touching upon black support for Williams were conducted on behalf of Kenney about two weeks ago. They showed about 44 percent of black voters lining up with Williams and 27 percent crossing over to Kenney and Abraham.

By comparison, those same polls showed about 11 percent of white voters casting ballots for Williams or one of the other African American candidates in the race - T. Milton Street Sr. and Doug Oliver.

A 27 percent African American crossover vote would be unexpected in Goode's view.

"There will be a crossover vote, but I don't think it is going to be as huge as some people think it is going to be," said Goode, who pegged it at 20 percent ultimately.

Williams looks to suffer some loss - if small - of that vote to Street and Oliver.

"It may be a close race that hinges on who is able to get their voters out to vote," Goode said.

That could be made more difficult by the general lack of enthusiasm some are reporting from the field.

"Despite all of the coverage and candidates' forums, there is a broad lack of enthusiasm for this election," said Bruce Crawley, a politically active African American public relations executive. "That is not just in the African American community, but across the board."

"I asked my committee people the other night, 'What are people feeling about the mayor's race?' " said Greg Paulmier, Democratic leader of the 12th Ward in Germantown, which is about 90 percent African American. "I didn't get a response. From anybody. My sense is people are not excited by the candidates."

Calvin Tucker, Republican leader of the 22d Ward and chairman of the Philadelphia Black Republican Council, had a similar sense of his Democratic neighbors in Northwest Philadelphia.

"There is some voter fatigue in regard to the African American vote," he said. "People are asking, 'What specifically has an African American brought to the table for the African American community?' When you look at the unemployment rate, the lack of homeownership, economic distress in the community - those problems are still there, despite the fact that we have had three African American mayors."

Crawley concurred there was a lack of confidence among African Americans that their votes could trigger meaningful change.

"I don't think people have seen very much get down to their level that has justified all the enthusiasm that went into recent federal-level elections," Crawley said, referring to the energetic response by black voters to the historic presidential candidacy of Barack Obama. "And they are feeling the same thing locally."

In this election, as in others, Crawley said he expected black voters to "give the African American candidates the first look," but not the only look.

"African American people will tend to vote for a qualified African American," he said, "but they are not going to vote for somebody who does not demonstrate ability."

That somewhat echoed Stewart's thinking as he sat in the sun on a bench at Ogontz Avenue and Walnut Lane last week.

"I want someone who is going to represent everyone in Philadelphia equally," he said. "Not just the upper class or just Chestnut Hill. I want someone who will represent the whole city."

Pressed, he said he did not yet have a preference, although he was most familiar with Kenney, because of Kenney's 23 years on City Council.

He was aware Kenney had the support of Evans and Tasco, two of Northwest Philadelphia's most powerful and successful African American elected officials.

"They have their recommendations," Stewart said. "At the end of the day, you have to determine for yourself which candidate you want to vote for."

He pondered a bit more.

"I have a moment yet," he said, giving nothing away.