President Trump 'inviting' a Republican or independent challenger in 2020: Sen. Jeff Flake

The retiring Arizona Senator and top Trump critic discusses the state of the GOP with ABC News chief White House correspondent Jonathan Karl.
10:13 | 12/24/17

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Transcript for President Trump 'inviting' a Republican or independent challenger in 2020: Sen. Jeff Flake
That's Arizona senator Jeff flake sitting right next to the president three weeks ago. The president presenting a unified front. When in reality, they have been feuding since the campaign. Flake works announced this fall, that he'll retire from the senate next year has been a constant critic of the president. Most recently over his support for judge Roy Moore's failed not campaign. Flake wrote a check for the Democrat, Doug Jones, tag it country over party. I sat down with flake to talk about his future and the future of his party. We began with the fallout from Alabama. The president was all if at the end for Roy Moore. The Republican national committee supported him financially. Is this a permanent stain on the party? I hope it's not permanent. It will be lasting. That will be used by the Democrats. If we were the Democrats, we would do it, too. So it will certainly be used by the other side and T's not -- wasn't our best foot forward, by any means. Steve Bannon was supporting Moore from the start. And by all accounts, helped convince the president, though I don't know if he needed much convincing, to support Moore. What is Bannon's role in the party now? I hope test been marginalized. The last thing we need is to push that -- ultra nationalist -- ethno-nationalist, protectionist element of the party. It's not good for us. What is the risk if the party continues in that direction? The Bannon direction. The trump direction. Could you lose the senate? Most definitely. You look at the audiences cheering for Republicans sometime. You look out there and say, those are the spasms of a dying party. When you look that the lack of diverse si sometimes. And it depends on where you are, obviously. But by and large, we're appealing to older white men. And there are just a limited number of them. And anger and resentment are not a governing philosophy. So you have to actually govern and do something. Sooner or later, the voters will figure out, I think they are and have, that, you know, you have to have something else. Reporter: Senator flake, a life long Republican, did not vote for president trump in 2016. So what about the president himself? First of all, do you -- what do you think the odds are that he doesn't seven out all four years? I don't know. The talk of impeachment. And what not. I don't get caught up in that. There's a lot of it on the left. So -- we'll see. We'll see what goes forward. I don't -- I look at the last campaign and -- and think, was that campaign even capable of colluding with anybody? It was so chaotic and what not. But the problem is it's always, as they say, the coverup. And the sensitivity that the white house has to the special counsel and the investigation is troubling. I still cannot figure out the rationale for the timing of the Comey firing. And if the president tries to continue to undermine the legitimacy of the investigation. If Republicans continue to try to help with that, I think that puts us in peril. We shouldn't participate many the undermining of our institutions that way. You look at the firing of Comey and what Comey said the president said regarding the Flynn investigation. The cost of key fig glurs the congress to back off of the investigation, is there already, layman's terms here, already an obstruction of justice to be made? No, I would wait for the special counsel, if the he's going to make that case, to make that case. I'm not prepared to make it. What if the president fires the special counsel? It will be a big problem. I don't think that will go over well at all. I don't think he'll go there. He should gotten there. And if he does? We'll cross that when he comes to it. I don't thing it would be received well here. Not by me. And if he pardons Michael Flynn. That is equally troubling. If it's part of the investigation, as way to circumvent the invest somehow, that would be very troubling. Reporter: Senator flake has called on Republicans to serve as a check on president trump. It's up so us to stand up and say, this is not acceptable. Reporter: Pu just a few weeks ago, he was there at the white house, sitting next to the president. Is there the froup of wonderful Republican senators is here to discuss the tax bill. Very importantly, we're going to be talking about trade nachbd that. There you are. You're with the president face to face. Did you use the opportunity to confront him on any of the things you have confronted him on? Certainly. On nafta. Some people expect that if you disagree with the president on some things, I do quite vociferously sometimes on policy things and some of his behaviors. But, that doesn't mean that I should try to hobble him. There's an op-ed written it was my responsibility. Well, because you have said -- on so many of the big issues. You supported him on the the Obamacare repeal. The tax cuts. You voted with him the overwhelming majority of the time. Put it this way, before the president came along, on health care reform, repeal and replacement of Obamacare, I voted on it some 40 times. Should I change just to spite the president? Same with regard to tax reform. I have been pushing corporate tax reform for years. Should I now turn the other direction just because the president happens to share our view? On the things we disagree on, the Muslim ban. During the campaign. Later changed to a -- a travel ban. Now I do believe it's constitutional. It's just not wise. I speak up. Every dhans I get, against that. Nafta. Getting out of nafta would be a disaster. Tpp, to exit that trade agreement, disaster. Those things I'll continue to speak against. Reporter: Now the outspoken senator who already made headlines with his stunning resignation speech -- We must stop pretending that the degradation of our politics and the conduct of some in our executive branch are Normal. They are not Normal. Reporter: He's set to give a series of speeches on the senate floor about the state of the uniyou known. The first one you want to do is about trump's relationship with the truth. What do you mean? We need, as a democracy, as a country, a shared facts that we can agree on. We need to know and people need to understand that our institutions are solid and durable. When we undermine them by talking about alternative facts or talking about statements that are just demonstrably false. Like I would have won the popular vote, for example. Or our institutions are sick. And -- that there's a rigged similar. Talking about electoral system. That's just not good. It's not right. Are you saying the president's a liar? I'm not saying that. Why not? You're saying what he says is not true. Isn't that what you're saying? We can all choose our own words. Reporter: He continues to serve in the senate until his term sup, just over a year from now. Giving him the opportunity to help push trump a ps agenda through. Or stand in the way. Does he have presidential ambitions of his own. That's not in my plans. I do wonder and I do worry that in the future we'll faced with -- president trump running for re-election on the one side. Drilling down hard on a diminishing base. And on the other side, you might have -- on the other side, you might have somebody like Bernie Sanders. Or Elizabeth Warren on the far left of the democratic party. That leaves a huge swath of voters. In the middle. That may be looking for something else. You're open to running for president in 2020? I don't rule anything out but it's not in my plans. It's coming up, by the way. It is. Would you be more likely to run for the Republican nomination against the president or as an independent candidate? I haven't thought that deeply about it. Like I said. But I do -- I do believe if the president is running for re-election, if he continues on the path that he's on, at the that's going to leave a huge swath of voters looking for someone else. If he's the Republican nominee again, we're likely to see an independent candidate. He's probably inviting a Republican challenge as well. Certainly an independent challenge. What would it take for you to leave the Republican party? You have already been harshly pr critical of your party's president? I can say the fact that Roy Moore lost his election is a good sign that maybe the Republican party, maybe we can turn back. If we continue the to go down that path, just to drill down on the base, think you'll have a lot of people realize there is no future for them in this party. I know a lot of them. Some are family members. Some are -- are -- you know, Republicans I have known for a long time. We have been life long Republican who is simply say this is not my party. This is not where I want to go. I hope, like I said, with the election results in Alabama, that maybe the party's realizing that, we have to change.

This transcript has been automatically generated and may not be 100% accurate.

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