Polls show that nearly half of those likely to vote in the District’s April 1 Democratic primary could change their mind about their choice for mayor in the final days of the race.

On Wednesday night, WUSA9 invited the top four contenders to make their last televised pitch to the electorate in an hour-long debate that had the candidates squabbling, throwing jabs and trying to talk over each other and moderator Bruce Johnson.

Mayor Vincent Gray tried to fend off allegations that he is corrupt, while his leading opponent, D.C. Councilmember Muriel Bowser, disputed claims that she is not prepared for the city’s top political post.

“Uncle Earl” — a nickname federal prosecutors say was used to refer to corrupt campaign financier Jeffrey E. Thompson during Gray’s 2010 mayoral race — loomed large in the first quarter of the forum.

Gray admitted to a phone call with Thompson, saying he asked for support from the local businessman and prolific fundraiser, but was initially turned down. Gray said he got a different answer when the two met later face-to-face.

“He said that he then would support my campaign. I asked him to do that, and he said, ‘yes,’ ” Gray said, rejecting the scenario that Thompson detailed in court as part of his guilty pleas to two counts of corruption. Thompson claims that Gray handed him a one-page budget for more than $400,000 of get-out-the-vote efforts.

“I never asked Jeff Thompson for $400,000,” Gray repeated.

Despite a Washington Post poll and NBC4/Marist poll showing Bowser running neck-and-neck with Gray, much of the debate stayed focused on the incumbent’s trustworthiness and his record.

Councilmember Tommy Wells, who represents Ward 6 and lives on Capitol Hill, continued to repeat his focus on bringing ethics back to city government. “This debacle has cost us at least $40 million,” Thompson said of the U.S. Attorney’s investigation into the 2010 campaign.

Defending Gray as “innocent until proven guilty,” councilmember Jack Evans, who represents Ward 2 and lives in Georgetown, said Gray’s other opponents were only arguing, “I should be mayor, because he shouldn’t.” He asked voters to look at his 23-year-record as a lawmaker.

The four candidates delved into education, solutions for the city’s homelessness crisis, fire and ambulance services and the speeding cameras that irk many D.C. drivers; a few of the candidates themselves have been issued tickets.

When the topic turned to experience, the debate devolved to a shouting match. Gray and Evans touted themselves, and each other, as the only two prepared to lead a city government with more than 33,000 employees and an $8 billion budget.

“You haven’t run anything,” is a frequent refrain of Bowser’s critics. Gray’s campaign this week launched the attack website “Muriel Not Ready,” bashing her as inexperienced.

Bowser, 41, accused opponents of questioning her ability to lead because she is “young and a woman.”

“People ask me that question all the time, when the fact is, I’ve been in local government for 17 years,” Bowser said. Policy jobs in Maryland government, work as an advisory neighborhood commissioner and her seven years on the D.C. Council give her experience on all sides, she claims.

Those four, plus candidates Andy Shallal, Vincent Orange, Reta Jo Lewis and Carlos Allen, have been invited to face off Thursday night at Sixth and I Historic Synagogue.