PHILADELPHIA - At what was billed as a forum on education issues, two of the Democratic candidates for governor on Wednesday night challenged primary front-runner Tom Wolf's judgment for standing by two friends who became mired in separate high-profile criminal cases.

Rob McCord, the state treasurer, questioned why Wolf agreed to chair the 2001 re-election campaign of then-York Mayor Charlie Robertson, who was charged with murder in the fatal shooting of a black woman during the city's 1969 race riots. Robertson, who had been a police officer at the time of the riots, dropped out of the race and was ultimately acquitted.

"What were you thinking when you failed to step away from Charlie Robertson?" asked McCord. The treasurer cited the NBA's lifetime ban of Los Angeles Clippers owner Donald Sterling, who was caught on tape making racist comments, as an example of how racist behavior should be dealt with.

"We need to have a governor who knows racism when he sees it," said McCord, whose wife is black.

Wolf, a York businessman and former state revenue secretary, replied that he counts Kim Bracey, York's first African-American mayor, as a supporter of his campaign and is proud of his work to put the city's racial strife of three decades ago behind it.

"I think the real issue is that York did go through some tough times and, as a native Yorker, I was deeply involved in those times and I'm proud of where we've come as a community," said Wolf.

U.S. Rep. Allyson Schwartz jumped in after McCord dropped his bombshell in the very first statement of the two-hour debate, which focused on the four candidates' pledges that included fighting for more money for schools, devising a fairer distribution formula and making charter schools toe the line.

"I do think we need a better answer from Tom Wolf on what happened," she said.

Schwartz also questioned Wolf's public support for former state Rep. Stephen Stetler, D-York, after he was convicted of corruption and sent to prison. Stetler was released in February.

"He defended someone who has already been convicted as a state representative, gone to jail and is working to overturn his conviction so he can take his pension."

Wolf has said he grew up with Stetler and joined other York leaders in contributing to his defense fund.

Wolf has contributed $10 million to his own campaign - nearly half of which came from a personal loan - that helped finance a TV advertising campaign that catapulted him into front-runner status.

McCord and Wolf lingered together on the stage at the Free Library of Philadelphia after the other candidates left, seeming to talk amicably for several minutes.

The other candidate, former state environmental protection secretary Katie McGinty, did not get involved in the discussion, but participated enthusiastically in the debate.

"If you want somebody who knows how to fight hard, but also have a little fun, then I'm your candidate," McGinty said.