Cohen, 52, who served by Trump's side as a Trump Organization executive and personal attorney for more than a decade, will call the president a "racist," a "cheat" and a "con man," according to a copy of his prepared remarks obtained by NBC News.
He will provide what he says are checks showing that Trump and his son Donald Trump Jr. personally reimbursed him for the $130,000 hush-money payment to porn star Stormy Daniels on the eve of the 2016 presidential election to keep her from speaking publicly about an alleged affair. Those checks came after Trump became president, Cohen will say.
And he will allege that Trump knew in advance that whistle-blowing organization WikiLeaks was planning to release hacked Democrats' emails in the late stages of the 2016 election that would be damaging to Trump's rival, Hillary Clinton.
Cohen has already pleaded guilty to multiple charges lodged by federal prosecutors in New York and special counsel Robert Mueller's probe of Russian election meddling and possible Trump-campaign collusion. His crimes included tax evasion and lying to Congress, as well as violating campaign finance law through his payment to Daniels.
He is scheduled to begin a three-year prison term in May. Nothing Cohen says before the House Oversight Committee can help him reduce that sentence.
Trump, who is in Vietnam meeting with North Korean dictator Kim Jong Un in pursuit of progress on denuclearizing the Korean peninsula, attacked Cohen's credibility in a tweet early Wednesday.
It is incorrect to claim Cohen's testimony to Congress would reduce his prison sentence because based on the committee's parameters, nothing Cohen is expected to say to Congress will reduce the sentence.
Republicans on the Oversight Committee also will likely hammer Cohen's credibility, highlighting the fact that he has already admitted to misleading Congress in prior testimony.