Michael Cohen, former personal lawyer to U.S. President Donald Trump, center, arrives to testify before the Senate Intelligence Committee in Washington, DC, U.S., on Tuesday, Feb. 26, 2019.

President Donald Trump's former personal lawyer Michael Cohen is expected to tell lawmakers this week about alleged criminal conduct Trump committed while in office, NBC News reported, citing a knowledgeable source.

Cohen starts a three-day gauntlet of congressional appearances on Tuesday by giving a closed-door interview to the Senate Intelligence Committee. He is expected to detail what he claims to know about Trump's contacts with Russia, hush payments made before the 2016 election and other sensitive matters.

Cohen arrived on Capitol Hill on Tuesday morning just as Air Force One delivered Trump to Vietnam, where the president was set to hold high-stakes talks with North Korean leader Kim Jong Un, adding more of a symbolic charge to an already historic moment.

Cohen is expected to provide evidence of alleged criminal conduct by Trump since he became president, NBC News said. In addition to his testimony, Cohen will reveal information about Trump's financial statements, according to NBC, citing a source who declined to be named.

The former Trump lawyer and fixer, who is slated to report to federal prison May 6, will also testify in a closed-door hearing with the House Intelligence Committee on Thursday. The main event of the week will happen Wednesday, however, as Cohen is scheduled to testify in public before the House Oversight Committee.

The White House pre-emptively trashed Cohen's testimony, calling him a "disgraced felon."

"Sadly, he will go before Congress this week and we can expect more of the same," Trump press secretary Sarah Huckabee Sanders said in a statement. "It's laughable that anyone would take a convicted liar like Cohen at his word, and pathetic to see him given yet another opportunity to spread his lies."

In his testimony , Cohen is prepared to describe behind-the-scenes anecdotes about Trump that include lies, racism and cheating as a private businessman when Cohen worked for him for 10 years, NBC News said, citing the source.

Likewise, Cohen plans to tell lawmakers that Trump asked him several times about a proposed skyscraper project in Moscow long after he secured the Republican presidential nomination, a person familiar with the matter told Reuters.

Cohen's assertion that Trump was inquiring about the project as late as June 2016, if true, would show Trump remained personally interested in a business venture in Russia well into his candidacy. Cohen, scheduled to report to prison in May after pleading guilty to charges including lying to Congress, has already said he briefed Trump on the project in June 2016.

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