After easily turning aside his primary challengers Tuesday, Mayor Luke Ravenstahl took the day off.

History suggests he had good reasons to put his feet up. It's been more than half a century since a Pittsburgh mayor lost a general election. At least two, and possibly more, candidates plan to challenge the mayor and that history this November. But they face daunting political and financial hurdles to turning the election into a real race.

Kevin Acklin, a Squirrel Hill lawyer and former Republican running as an independent, and Franco "Dok" Harris, a Shadyside businessman who has also announced an independent bid, both contend that Mr. Ravenstahl is vulnerable in November. But, insofar as there is an anti-Ravenstahl vote out there, his opponents' challenge is compounded by the fact that they will be dividing it. And, depending on the still-pending results of Tuesday's balloting, the anti-incumbent pie may be split further.

The city's voter rolls contain 175,283 registered Democrats and 31,236 registered Republicans. In a primary with a notably low turnout, Mr. Ravenstahl got 26,848 votes, or 59 percent Tuesday -- more than twice as many as his two opponents combined.

Mr. Ravenstahl said he will continue an "aggressive" campaign through November, even while juggling the city's new Act 47 recovery plan, its calls for new taxes and looming contract battles with city unions.

"We've talked about our vision and plan for the future of the city, and that's what we're going to continue to do. I believe we ran a very good and aggressive campaign in May, and plan to do the same in November," he said.

Two years ago, Mark DeSantis won the GOP nomination on the strength of write-in votes. In an overwhelmingly Democratic city, his was the most well-financed general election mayoral challenge in decades. He managed to attract just about one vote in three and won only two of the city's 32 wards -- the 7th, Shadyside, and the 14th, Squirrel Hill. Shadyside and Squirrel Hill once again formed the core of anti-Ravenstahl strength on Tuesday. And those, coincidentally or not, are the homes of the mayor's remaining challengers.

To get to a November plurality, Mr. Ravenstahl's new challengers would have to forge a message that will resonate beyond those relatively affluent East End neighborhoods, attracting support in black communities and the populous wards south of the rivers. Mr. Acklin and Mr. Harris insist that it has the potential to be a genuine competition. Others, even those sympathetic to the mayor's challengers, are reserving judgment.

"The DeSantis base has been identified, but you can't stay there," said Councilman Doug Shields, who considered running this year and who was a key adviser to the last mayor to win a full term, the late Bob O'Connor. "You have to go to the South Hills, to places like Carrick. You have to realize there is a lot more to the city than a couple of East End wards."

Councilman Bill Peduto knows the odds. He lost to Mr. O'Connor in 2005 and considered but dropped a challenge to Mr. Ravenstahl two years ago. Asked whether he foresees a credible November challenge for Mr. Ravenstahl, he said, "That depends on the other two. Will they have a real campaign with a field presence, with fundraising and a little bit of drama? Will they have the ability to create opportunities in the ... media that stir peoples' imaginations?"

The challengers say yes.

"You can look at the numbers and ... you can say this is crazy. This is a Democratic town; you're not a Democrat ... Why would you do this?" said Mr. Acklin. "I do it because in my opinion, the emperor has no clothes; there's just not a lot of leadership there."

Mr. Acklin, at 33, the old man in this field, said he has a few ways of changing the poor pattern for mayoral challengers. He has forged community ties through a nonprofit he started last year called ReNew Pittsburgh, which sponsors volunteer cleanup efforts citywide. And he has family bonds to the city workforce -- his grandfather and uncle were city firefighters and his mother was among the first women to take the firefighter test, though she didn't join the department. His stepfather is in the city's Public Works Department, and his younger brother is a state trooper.

"When you're out there every day and you're working with people and you're meeting with people in the community, you see the games that are played. You see what I'd call a sort of governance by photo ops," he said last week.

Like Mr. Harris, he has an impressive educational resume but a relatively thin political background. The South Oakland native, who is married and has two young boys, graduated from Central Catholic High School. He went to Harvard University on scholarship, playing defensive end for its football team, then got his law degree from Georgetown University. He worked for Republican Gov. Tom Ridge and for a Boston law firm before resettling in Pittsburgh in 2003.

In 2007, he improbably lost the race for the Republican at-large seat on County Council to Charles McCullough. Mr. McCullough announced that he was suspending his campaign after reports which would eventually lead to his indictment on charges that he had stolen from the estate of an elderly woman. The voters elected him anyway.

Two months ago, Mr. Acklin dropped his Republican registration, a legal requirement for anyone running as an independent. He said he did so to prove that he is nonpartisan. More pragmatically, he also knew that running as a Republican was a sure loser.

"There is a race to be run as a Republican. It's probably a losing race that builds name recognition for something in the future. That's not a race I want to run," he said.

His campaign raised nearly $56,000 through May, with hopes of raising about $300,000 through fall. His biggest donor was FamilyPAC, a Federated Investors political action committee that usually supports conservatives, and Federated executive Christopher McGinley.

He is taking a leave from his law firm, Morgan Lewis & Bockius, starting June 1 to dedicate himself full time to the race. He has hired staff and is opening campaign offices in the South Side and elsewhere.

"With some more time, some more effort, some more visibility in the neighborhoods, I think we have a shot. There will have to be some lightning strikes and some luck, but it's definitely worth it," he said.

Mr. Acklin has already filed nomination papers with the 1,119 signatures needed for an independent candidate to secure a place on the November ballot. Mr. Harris has yet to follow suit, but he, like any other unannounced candidates who may be out there, has ample time until the Aug. 3 deadline.

Mr. Harris, 29, a North Side native, graduated from Sewickley Academy in 1997 and Princeton University in 2001 with a degree in politics. After working in banking in Washington, D.C., he returned to Pittsburgh to enter the joint law-business degree program at the University of Pittsburgh and Carnegie Mellon's Tepper School of Business. He graduated last year and works for Super Bakery Inc., the business owned by his father, Steelers Hall of Famer Franco Harris.

He argues that his business background would allow him to bring a more professional approach to city government with sounder management and a comprehensive (though still unspecified) approach to the long-term financial problems of city pensions and debt. He is aware of the history he is up against.

"For a long time, it's been viewed that the primary was the actual election. The Republican in November was a sacrificial lamb," he said.

So why will this year be different?

"Winning in November is doable," he said. "We've got the right professional team, the right volunteer base to really push the city."

Mr. Harris said he would demonstrate the qualities of transparency and reform he promises for city government with self-imposed contribution limits modeled on the donor ceilings for federal candidates. In the days before the primary, Mr. Ravenstahl signed legislation setting new contribution limits for city candidates, but they do not go into effect until next year.

Despite those limits, Mr. Harris said he's confident of meeting an ambitious fundraising target.

"Our goal, all in, by November, will be in the very high six figures," he said, although his fledgling campaign has yet to file a public spending report.

With that budget, and a lot of door-knocking and community events, he said he hoped to pierce the wall of apathy that he said was evident in the voter turnout that was low even by the traditionally modest standard of past primary elections.

"The discussion of economics was rather sparse," he said of the primary discourse. "It was more of a referendum on the mayor, but the city is in a bind right now," he said, adding that he hoped to steer the fall conversation toward longer-term solutions for city finances.

Mr. Acklin suggests that he or any challenger can run a credible campaign with a much lower dollar figure than Mr. Harris suggests. Mr. DeSantis, who ran the most expensive GOP mayor campaign of the modern era, leans toward Mr. Harris' view of the resources needed for a robust challenge.

"We raised and spent roughly $500,000 and we [managed] what was considered to be a minimal television and radio presence ... . I think you need at least a million to have a real presence media-wise, to have the kind of media campaign infrastructure."

Mr. DeSantis was able to reap free publicity from the multiple debate stages he and Mr. Ravenstahl shared two years ago. He said that to concentrate the voters' focus for the debates and the campaign in general, it would be a tactical advantage for one of the two independents to leave the field to the other.

"You aren't going to convince me that you could have a scenario with a three-way race and Ravenstahl losing," he said.