Michael Cohen, President Trump's former lawyer and "fixer".
Cohen also plans to tell USA lawmakers that Trump asked him several times about a proposed skyscraper project in Moscow long after he secured the Republican presidential nomination, according to reports.
This week, Cohen is set to make the three-day marathon of appearances before three congressional committees.
Cohen is also expected to provide some of Trump's private financial statements and give what the Journal called "behind-the-scenes" details of working for Trump, the Journal said. "Sadly, he will go before Congress this week and we can expect more of the same", Sanders said, adding: "It's laughable that anyone would take a convicted liar like Cohen at his word".
Speaking on Wednesday to a House of Representatives panel, Cohen will allege possible tax fraud and racist language by Mr Trump, say U.S. media.
According to a recent memo sent out by committee staff, Cohen's appearance before the House oversight panel will concern various financial issues related to the 2016 presidential campaign, including payments to adult film star Stormy Daniels and former Playboy model Karen McDougal that federal prosecutors in NY say were directed by Trump.
His in-depth discussions on Tuesday and Thursday with the intelligence committees of the Senate and the House of Representatives will be behind closed doors.More news: North Korea's Kim reported en route to Vietnam summit with Trump
More news: Jussie Smollett removed from this season's final episodes of 'Empire'
More news: Karl Lagerfeld, Chanel fashion designer, dead at 85
Critics noted that the tweet sounded a lot like Trump's own threats to Cohen, which many argued were clear instances of witness intimidation - a federal crime.
The Stormy Daniels and Russian Federation issues have been talking points for a long time now, but perhaps one of the most shocking aspects to Cohen's testimony will be the charge that Trump regularly employs racist language when talking about blacks.
"I'm sure there will be some questions we know the answers to, so we'll test him to see whether in fact he'll be truthful this time", Burr said.
Trump denies the allegations and says that Cohen lied to get a lighter sentence.
Cummings' panel will focus on Trump's debts and payments "relating to efforts to influence the 2016 election", as well as his compliance with financial disclosure, campaign finance and tax laws, it said.
Cohen's testimony comes ahead of his incarceration on a three-year prison sentence handed down in December after he pleaded guilty to bank fraud, tax evasion and campaign finance violations, and lying in earlier testimony to the Senate panel.
The House intelligence committee chairman, Adam Schiff, postponed Cohen's appearance before that committee, saying it was "in the interests of the investigation", with no additional details.