Transcript for Showdown brews on Capitol Hill over Trump's wiretapping claims
showdown brewing on capitol hill. The nation's most powerful law enforcement officer, FBI director, James Comey, set to testify before a senate committee, digging into Russian involvement in the 2016 campaign. Possibly making his first public comments also about president trump's so far unproven claim that president Obama wiretapped trump tower. The stakes are so high. We start tonight with David Wright. The truth, the whole truth and nothing but the truth. Reporter: One day before what promises to be a showdown on capitol hill. Have you seen any evidence that president Obama ordered an illegal wiretap? No, I haven't. Reporter: Lawmakers on the house intelligence committee are prepared to grill the nation's top law enforcement officer. One committee member already calling for president trump to apologize. It never hurts to say you're sorry. So you think president trump should say I'm sorry? I think so. Reporter: At issue is not just the trump tweets accusing Obama of a felony. Was there a physical tap of trump tower? No, there never was. No evidence to support the president's claim. Reporter: Also, the lingering question of whether the president's men may have colluded with Russia to influence the election. Democrats and Republicans see it differently. I would characterize it, there is circumstantial evidence of collusion. No, everything I have up to this morning. No evidence of collusion. Reporter: James Comey is in a position to know whether there's probable cause to support either story. He's become more famous than me. Reporter: The very same FBI director who grabbed so much attention himself during the 2016 campaign. First, closing the case against Hillary Clinton for using that private e-mail server for sensitive government business. Our judgment is that no reasonable prosecutor would bring such a case. Reporter: Only to reopen it nine days before the election. I have to give the FBI credit. That was so bad what happened originally, and it took guts for director Comey to make the move that he made. Reporter: After all that, nothing found. Until now, Comey has not spoken publicly. Hasn't even confirmed an investigation is under way. But he has briefed committee members behind closed doors. If Comey comes out and says, there was no wiretap, case closed, will president trump accept that? You'll have to ask the president that. David joins us live. A lot of anticipation for Comey tomorrow. And another important name headed to capitol hill, judge Neil Gorsuch. Reporter: That's right. President trump's pick for the supreme court begins his confirmation hearings tomorrow. Democrats are unlikely to give him an easy ride. David, thank you. Next to the nationwide manhunt for the high school
This transcript has been automatically generated and may not be 100% accurate.