D.C. mayoral candidate Muriel Bowser and Mayor Vincent Gray argue over why the funding scheme perpetrator used the alias 'Uncle Earl.' (WJLA)

D.C. mayoral candidate Muriel Bowser and Mayor Vincent Gray argue over why the funding scheme perpetrator used the alias 'Uncle Earl.' (WJLA)

Mayor Vincent C. Gray strolled out onto a new, much rougher campaign trail Thursday night, taking sharp verbal blows from two of his leading challengers in the Democratic primary race days after federal prosecutors unveiled new allegations about his knowledge of an illegal campaign scheme.

On several occasions, a feisty Gray told his foes that if they had evidence he committed a crime, to “put it on the table.”

The scrapping took place in the first and only major televised debate ahead of the April 1 primary, aired on NewsChannel 8. The proceedings began with discussion of the federal investigation, which centers on Gray’s 2010 mayoral campaign, and the focus remained there for much of the hour-long program.

“The entire election was corrupted,” said D.C. Council member Muriel Bowser (Ward 4). “I do believe the U.S. attorney when he says that. It’s also hard to believe that $600,000 . . . could be missed by a candidate — especially a candidate who is known for his attention to detail.”

Prosecutors alleged Monday that Gray had knowledge of an unreported “shadow campaign” of that scale waged on his behalf by businessman Jeffrey E. Thompson, who pleaded guilty to conspiracy charges in connection with that and other efforts to subvert campaign finance laws.

Gray has denied wrongdoing, calling allegations that he knew about the effort “lies” and suggesting that Thompson manufactured his story in order to win a favorable deal from prosecutors. He continued to do so Thursday.

“I don’t think the truth has come out in this situation,” Gray said. “You look at the quote-

unquote punishment that was meted out to Mr. Thompson, and one has to question how you could be involved in 28 separate elections in the way he was . . . and end up getting a punishment of six months of house arrest.”

Of the eight Democrats who will appear on the primary ballot, the debate included the four who have led in recently published polls. For candidates who have become accustomed to the rote repetition of talking points at genteel community forums, the smaller field and intimate confines of a television studio made for a much sharper and more freewheeling exchange.

At numerous points, the candidates talked over one another and host Bruce DePuyt, occasionally pointing fingers and making only intermittent eye contact.

Council member Tommy Wells (Ward 6) questioned Gray’s credibility, noting that a mutual friend, Thomas Gore, had pleaded guilty to a felony charge related to the coverup of illicit cash payoffs to a minor 2010 candidate, Sulaimon Brown.

Wells said it was “hard for me to believe” Gray had no knowledge of the scheme.

“Well, it’s a fact, Tommy,” Gray replied. “So if you have some information to the contrary, put it on the table.”

“He got the job,” Wells said, referring to the six-figure post Brown briefly held after Gray’s inauguration.

Less aggressive was council member Jack Evans (Ward 2), who lamented the slow pace of the ongoing federal probe and the “cloud” over the mayoralty but otherwise declined to attack Gray over the new allegations. Unlike Bowser and Wells, he has not called for Gray’s resignation.

Evans compared the investigation to the Whitewater probe of President Bill Clinton, which dragged on for years: “Is that what we’re facing here?” Evans asked. “For the good of the city, this has got to come to an end one way or another.”

It was Evans, not Gray, who tried — unsuccessfully — to turn to other matters early in the proceedings. He was more interested in undermining Bowser and Wells, questioning the former’s management experience and mocking the latter’s emphasis on campaign finance reform.

“Nobody on the council stood up for you because nobody wanted to,” Evans said, referring to a 2012 vote to change Wells’s oversight responsibilities. “Maybe it’s because nobody liked you.”

Wells, meanwhile, tried to paint Evans and Bowser as part of the same “pay-to-play” system that produced the shadow campaign, and he touted his own refusal to accept corporate donations in his current campaign.

Gray, after fending off months of specific questions about his knowledge of the shadow campaign, said he learned of its existence from his lawyer “long after it was over.”

Asked why he had not disclosed that sooner, Gray said, “I follow the advice of my attorney, and that’s the advice that he gave me.”

DePuyt asked Gray about his use of a code name, “Uncle Earl,” for Thompson to shield his identity. “He did this with other candidates, like Muriel Bowser,” Gray said.

“No, sir,” Bowser said, setting off a heated exchange that included Gray suggesting that she had once referred to Thompson using a similar term at a fundraiser.

“Did he ever ask you to refer to him as ‘uncle’?” Gray asked. “That’s what a lot of people think.”

“Mr. Gray, don’t switch this to us. Muriel Bowser is not the subject of the U.S. attorney. You are the subject of the U.S. attorney,” she said.