Grimm is challenging Donovan in the Republican primary to win back the seat for New York’s 11th District.
Grimm represented the 11th District before resigning in 2015 after pleading guilty to tax evasion related to a health food restaurant he ran.
Grimm subsequently was sentenced to eight months in prison.
Donovan was then elected in a special election in 2015.
Donovan mentioned Grimm’s criminal record in the opening remarks at the College of Staten Island on Thursday, according to the New York Post.
“My opponent lied to our community, asked us to vote for him, and then used our vote to cut a deal with the Justice Department,” he said.
Conversely, Grimm hit Donovan for using his office as his living quarters in Washington.
“I’m running again,” he said, “because over the last three years my opponent hasn’t just been sleeping in his office, he’s been sleeping on the job.”
Donovan also hit Grimm for a fundraising scandal with Grimm’s ex-girlfriend Diana Durand, whom Donovan called an “unwed mother,” that landed Durand in prison.
The debate was not as heated as their debate earlier in the week, where the two clashed about the possibility of President Donald Trump pardoning Grimm.
New York’s primary is on June 26.
Trump endorsed Donovan in a tweet where Trump flubbed the facts on Donovan’s voting record.
Similarly, Trump’s lawyer and former New York City Mayor Rudy Giuliani also endorsed the incumbent and will campaign with Donovan Saturday.