Transcript for Michael Cohen arrives on Capitol Hill today to testify
unfolding drama back home. President trump walking down the steps of air force one, fully aware that back home, they are watching something else unfold, too. His former personal attorney and fixer Michael Cohen walking toward the senate hearing room today to start three days of questioning. Tomorrow, he'll be before the American people. And tonight, what we've learned here, what Cohen is going to say about his former boss. On his finances, his worth and it is believed Cohen will accuse the president of criminal conduct. ABC's Mary Bruce leading us off tonight with the dramatic day on the hill. Reporter: Michael Cohen, who once said he'd take a bullet for Donald Trump, arriving on capitol hill today to unload on the president. Mr. Cohen, should the president be worried? What evidence do you have of criminal conduct? You've lied before, why should congress trust you now, Mr. Cohen? He spent hours behind closed doors with the senate intelligence committee. But tomorrow, he will testify in public, describing, according to sources, the president's, quote, "Lying, racism and cheating." And for the first time, he will accuse the president of criminal conduct while in office and provide what he says is a dramatic reversal for the man who stood at the president's side for a decade. I'm obviously very loyal and very dedicated to Mr. Trump. Reporter: Cohen has pleaded guilty to a host of crimes, including breaking campaign finance laws by paying hush money to porn star stormy Daniels just 11 days before the election. President trump initially claimed he knew nothing about it. Why did Michael Cohen make it if there was no truth to her allegations? You have to ask Michael Cohen. Michael is my attorney and you'll have to ask Michael. Reporter: But prosecutors say the president actually directed Cohen to make those payments. And tomorrow, Cohen is expected to say just that. Do you have any concerns about Michael Cohen's testimony before congress this week? No, no. Reporter: Cohen will also explain why he lied to congress about a trump tower deal in Moscow. A project he now admits trump's team was negotiating well into the campaign. Sources say he will also produce some of the president's financial statements, which he says show trump made false claims about his net worth. And tonight, Republicans are on the attack. Congressman Matt Gaetz, a trump ally, tweeting what seemed like a threat to reveal embarrassing personal information about Cohen. Saying Cohen's wife is "About to learn a lot." We're witness testing not witness tampering. And when witnesses come before congress, their truthfulness and vor rasty are in question and we have the opportunity to test them. Reporter: But Cohen tonight, undeterred. A source close to him insisting, "Facts will come out tomorrow, and no amounts of threats against Mr. Cohen and his family or baseless smears can change them." Mary Bruce, we saw in your report there, the president's allies on the attack against Michael Cohen. And tonight, the white house lashing out, as well? Reporter: David, Republicans and the white house are trying to discredit Cohen's testimony by pointing out that he has lied to congress before. The white house press secretary saying, quote, it's laughable that anyone would take a convicted liar like Cohen at his word. But David, members of the senate intelligence committee tonight tell us this was a serious grilling and the Cohen that showed up today was, quote, a very different guy. David? Mary Bruce leading us off tonight. Mary, thank you. And we should note, ABC news will have live coverage of the Cohen hearing tomorrow at 10:00 A.M. Eastern right here.
This transcript has been automatically generated and may not be 100% accurate.