Transcript for Latest DC developments from Trump endorsing Roy Moore to Flynn's guilty plea
Breaking news in the Russia investigation. We begin with president trump and his words for Michael Flynn. Michael Flynn pleading guilty to lying to the FBI. Reporter: Today in Washington, a news blizzard. Massive storms brewing on several fronts. The trump white house the center of it all. In congress, a hotly contested tax bill on the verge of becoming law. Historic tax relief as a giant present for Christmas. Reporter: In Alabama, a pivotal senate race rife with controversy down to the wire. Tonight the supreme court finally allowed the most recent incarnation of the president's long-delayed travel ban to take effect. And of course, overshadowing it all, there's the Russia investigation. I think what we're beginning to see is the putting together of a case of obstruction of justice. Reporter: On any given night, any one of these stories could be leading the news, but in the trump era, it's all coming at you at once. This latest news storm started Friday with Michael Flynn. He pled guilty to lying to the FBI. That's a felony. Now he's helping the special counsel. No, I'm not. Reporter: The president insists he has nothing to fear. What has been shown is no collusion, no collusion. There's been absolutely -- there's been absolutely no collusion. Reporter: Possible collusion may not be his only problem. On Saturday morning this tweet from the president set off a firestorm because it seemed to suggest for the very first time that trump knew Flynn had committed a crime when he fired Flynn. Quote, I had to fire general Flynn because he lied to the vice president and the FBI. That's potentially significant. Do you solemnly swear to tell the truth, the whole truth and nothing but the truth so help you god. Reporter: Because former FBI director James Comey has given sworn testimony that trump asked him to go easy on Flynn. I understood him to be saying that what he wanted me to do was drop any investigation connected to Flynn's account of his conversations with the Russians. Reporter: Comey didn't back down. Trump ultimately fired him, too. Trump insists he never pressured Comey to stop investigating him. The more the president knew about what Flynn said to the FBI before he took action on Comey, the more perilous it is for him. But there still remains an argument that you're going to need more than just he fired Comey because of the Flynn investigation. Reporter: The white house scrambled to distance the president from that Saturday tweet. Trump's lawyer insisted he drafted it for the president. Another white house official called it sloppy. The president also went on the attack, accusing Comey of running the FBI into the ground, its reputation is in Tatters, he tweeted, worst in history. He also questioned the integrity of the special counsel's office after it came to light that Robert Mueller fired one of his top investigators in the Russia probe last summer for sending what were potentially anti-Trump texts to a colleague during the campaign. This morning trump brought up Clinton again, this time defending Mike Flynn. Hillary Clinton lied many times to the FBI. Nothing happened to her. Flynn lied and they've destroyed his life. I think it's a shame. Reporter: Today the white house legal team floated an extreme option, testing out a controversial new theory that a president cannot obstruct justice because he's the chief law enforcement officer and, therefore, has a right to express his view on any case. I think what the trump team is trying to do here is conflate the question of can he be charged with obstruction of justice ever with could he be charged with obstruction of justice for firing James Comey. Reporter: He has control of personnel. He can make decisions for whatever reasons he wants. The problem for them is, I think if there's an obstruction charge here, it's going to be based on a pattern of conduct. It's not just going to be based on firing James Comey. Reporter: All of this at the start of a week that has more bruising battles ahead. Early Saturday morning the senate narrowly passed tax reform, 51-49. The tax cuts and jobs act as amended is passed. Reporter: Not one Democrat voted in favor. We're talking about massive, massive tax cuts. Reporter: The house has already passed its version of the plan. The president is hoping to have a version of the bill that's acceptable to both houses on his desk before Christmas. This is a big legislative win, the most significant one for the trump administration thus far. And this is something to take home to your constituents. Reporter: Republicans insist the bill would pay for himself but the nonpartisan joint committee on taxation says the senate version would add $1 trillion to the deficit over the next decade. This bill is unpopular. It's being pushed by a very unpopular president and passed by a very unpopular congress. That's not a recipe for political success. This is what it looked like. Reporter: Democrats are calling it a tax cut for the rich that's being pushed through without giving lawmakers time to read it. Here are the modifications in it. I can read one word, "Add this language." Can you tell me what that word is? It's about 500 Hu h00 pages. Reporter: President trump needs every vote he can get which is one reason today he gave Alabama's Roy Moore his full endorsement. But seven women have accused Moore of sexual misconduct, some of sexual assault when they were teenagers and he was in his 30s. Mr. Moore attacked me when I was a child. Reporter: Allegations Moore denies. Today the president called Moore from air force one and told him, go get 'em, Roy. I think it's a mistake. I think it tarnishes the Republican brand and tarnishes the president to be associated with somebody that is an accused child molester. Reporter: A new CBS poll finds nearly 3 out of 4 Alabama Republicans, 74%, don't believe the allegations against Moore. The poll has Moore ahead by six points among likely voters. The issue hits home for the president, too, for obvious reasons. You can do anything. Whatever you want. Grab them by the . Reporter: After the off-color remarks from the "Access hollywo Hollywood" bus during the campaign, women came forward accusing trump of allegations. Allegations trump denied. Today Billy bush, the former tb host who shared trump's joke on the bus published an op-ed in "The New York Times." The president initially excused his words on the bus as locker room talk. That's locker room, that's locker roorm. Reporter: More recently he's questioned the authenticity of the tapes. Bush disputes him saying, yes, Donald Trump, you said that. And that he believes the women who accuse trump of groping them. Steve bush is on Steven colbe Colbert's show. Stop playing around with people's lives. Reporter: All of this and it's Monday. The week's just getting started. In the trump era, we never know what headlines tomorrow night bring. I'm David Wright for "Nightline" in New York.
This transcript has been automatically generated and may not be 100% accurate.