Michael Cohen, President Trump’s former personal lawyer, is scheduled  to report to the Federal Correctional Institute at Otisville, N.Y., on May 6 to begin serving a three-year sentence for infractions including lying to Congress, tax fraud, and campaign-finance violations in connection with bribe payments to an adult-film actress who claimed she had an affair with Trump.

He took the witness stand Feb. 27 before the House Oversight Committee, claiming that Trump directed him to lie about a hush money payment to Stormy Daniels, an adult film actress, He also said the president’s son, Donald Trump Jr., and the chief financial officer of Mr. Trump’s company, Allen Weisselberg, had arranged those payments.

Mr. Cohen also said he had lied previously to Congress about when then-candidate Trump stopped talking with Russian contacts about a proposed Moscow Trump Tower project.  He had earlier said that those discussions ended in January 2016, nine months before the general election, but in fact they continued throughout the campaign.

That is important because people have been trying to figure out whether Trump was offering to reduce sanctions against Russia, changing American foreign policy, in return for a favorable contract to build in Moscow. Some believe that Trump was putting his business interests ahead of U.S. political and security interests.  

One of the president’s lawyers, Jay Sekulow, said there was no truth to Cohen’s allegation.

“Today’s testimony by Michael Cohen that attorneys for the president edited or changed his statement to Congress to alter the duration of the Trump Tower Moscow negotiations is completely false,” Mr. Sekulow said in a statement Feb. 27.

President Trump himself said his pledge not to conclude new deals only applied after he had been elected and inaugurated. He was completely within his rights to continue to run his businesses even as he pursued his presidency, he said.  

But Mr. Cohen said that President Trump’s intentions were clear.

“Mr. Trump did not tell me to lie to Congress,” Cohen said. “That’s not how he operates. He would look me in the eye and tell me there’s no business in Russia and then go out and lie to the American people by saying the same thing. In his way he was telling me to lie about it.”

During his appearance before a House committee, Cohen delivered an account of his dealings with the man who he helped win the White House, saying President Trump is a “racist,” a “con man” and a “cheat. ”

Mr. Cohen’s credibility has been directly and frequently challenged by Republican representatives and supporters  of the president, who note that he is a recently convicted felon who lied to Congress two years ago about the same subject — what he had done on behalf of the president.

President Trump commented on Twitter.

“Michael Cohen was one of many lawyers who represented me (unfortunately),” President Trump tweeted Feb. 27.

“He had other clients also. He was just disbarred by the State Supreme Court for lying & fraud. He did bad things unrelated to Trump. He is lying in order to reduce his prison time.”