"I rise today to say, 'Enough,'" he told his colleagues, ripping the president of his party for policies and behavior he called "dangerous to a democracy."
Last month, Flake delivered a second Senate floor speech likening Trump's words to those of 20th century Russian dictator Josef Stalin. As he leaves his Senate seat, he has pointedly declined to rule out challenging Trump by running for president himself.
Yet he has not waged an all-out assault on the president's agenda. He joined fellow Republicans in delivering Trump's greatest victory so far, backing the $1.5 trillion tax cut despite his own expressed concerns about budget deficits.
Flake sat down to discuss his approach to challenging this White House, and his plans, in the Senate office that doubles as his living quarters when he's in Washington. What follows is a condensed, edited transcript of our conversation.
JOHN HARWOOD: You going to have a hard time giving up this bedroom, home sweet home?
SEN. JEFF FLAKE: Going to have to. I won't miss it.
HARWOOD: Have you done that the whole time you've been in Congress?
FLAKE: I'm cheap and poor. And even if I wasn't, I'd do it anyway. It's just easier.
HARWOOD: You are the former head of the Goldwater Institute.
HARWOOD: I saw a copy of "Conscience of a Conservative" over there. And I think you've always had a reputation as a person of principle in the Congress. There are lots of different kinds of principles. What are the most important ones to you at this moment?
FLAKE: Fiscal discipline, limited government. Being a conservative, I've always felt, was believing in limited government, economic freedom and individual responsibility.
HARWOOD: But there are ideological principles, there are principles of character, there are principles of national security. You've talked about threats to constitutional democracy and echoes of Josef Stalin. How important is that in your hierarchy right now?
FLAKE: Being a conservative is not just believing in limited government and economic freedom. It's being conservative in comportment and demeanor.
HARWOOD: But that sounds more like manners than about national protection. How big a threat do you perceive to the country from the political moment that we're in right now?
FLAKE: I think it's a big threat. Those are character traits, I guess, to be temperate and measured. But that's important for our allies, for trade partners, to know that we're going to be there, we're going to be reliable. And for our adversaries to know where we are. Instead we seem a little unreliable, or a lot unreliable.
And then we have the president using language that really is not becoming of the United States president, calling the press the enemy of the people, to see his term "fake news" used by authoritarians everywhere to justify cracking down on dissent. Those character traits that are conservative, that are really absent now, I think, put us in danger.
HARWOOD: Let me ask it differently. Do you think an authoritarian power overseas has managed to compromise the U.S. government?
FLAKE: No, I'm not saying that. I'm not one of those who run around calling for our president to be impeached. He's done nothing in my view that would warrant that. But I do think that the behavior he sometimes exhibits, and some of the policies that he has adopted, aren't good for our national security.
HARWOOD: What have you concluded about what Russia did, what the president did or didn't do with respect to that, and what danger that poses as a matter of national security?
FLAKE: Russia did interfere in our elections. It seems as if they did it to benefit one of the candidates. I'm not saying that that was dispositive, that's what made the difference. But that did occur. And what troubles me greatly is, I'm not aware of any Cabinet-level kind of meeting, or any high-level attempt to actually get a handle on this, and to figure out how we're going to respond.
HARWOOD: What do you conclude about whether the president or people close to him had anything to do with it?
FLAKE: I'm not among those who think that the president is compromised, or that they colluded …
HARWOOD: You're not?
FLAKE: No. Really, no. I don't think that the campaign colluded in some meaningful way. I don't think that they were organized enough, or competent enough as a campaign to do that.
It is troubling that they won't accept that that kind of intervention was happening on the part of the Russians and won't look to combat it. But I think it's more out of a sense of trying to protect his status as somebody who won the election.
I don't think it's, I'm beholden to them somehow, or worried that they have compromising material.
HARWOOD: So when people say (those) like you, who have criticized the president, have not taken action commensurate with the threat you identify, your answer is: You think that this is something that happened that the president did not help make happen, and therefore it's somewhat less grave.
FLAKE: Some people think, well, if you disapprove of some of the president's actions, or his behavior, then you ought to vote against everything that he supports. I don't view it that way. That's not my job.
HARWOOD: Ben Wittes and Jon Rauch wrote in The Atlantic recently that Trumpism is a threat to the institutions of the United States, Republicans have become the party of Trumpism, therefore everything he is trying to do needs to be stopped in the higher interest of protecting those institutions.
FLAKE: I understand that impulse. That impulse was there as soon as Barack Obama was elected. Now, you know, the tables have turned — kind of the same argument on the other side. There may come a point at which you say, hey, this is a grave threat, and you can't agree with anything the president does. We're not there.
HARWOOD: Do you consider Obama and Trump comparably benign in terms of the danger to the country?
FLAKE: There are a lot of things I disagreed with President Obama on with regard to foreign policy, and domestic policy as well.
It's not as if I think the president is intentionally trying to undermine our behavior. He has a different philosophy and is, I think, a bit careless sometimes.
HARWOOD: When you wrote a check to Doug Jones, the Senate candidate in Alabama, Democrat, you wrote, "Country over party."
HARWOOD: I just want to ask you about that in light of two votes you made recently: one for a partisan tax bill that increased the deficit, the other against a bipartisan spending deal that also increased the deficit. Were you picking party and ideology over (the) consensus view — country, if you will?
FLAKE: No. I would've written the tax bill much differently. I would've done the corporate tax reform, which we desperately needed — both sides of the aisle, really, knew that we needed corporate tax reform. I would have left the individual rates as they are.
HARWOOD: But you accept that it will increase the deficit.
FLAKE: In the short term, yes. But in the long term, I'm enough of supply-sider that I see the benefits there. With regard to the budget deal, oh my goodness, I don't know how in the world you can justify that.
HARWOOD: On the tax bill, one of the things you secured before voting the bill was a promise to do something about the "dreamers." Given where we are now, and given the prospects for actually getting a legislated solution, you could argue that you on DACA, just like Sen. Collins on marketplace fixes for health care, simply got taken.
FLAKE: No, I don't think so. You can't ever say, "I demand, for this vote, passage of my version of DACA." You can't do that. All you can say is, "I want a vote."
HARWOOD: Going back to country over party and the potential threat, do you think that to check and curb that threat, the country needs divided government right now?
FLAKE: I've said it many times before, the best formula for fiscal restraint is divided government.
HARWOOD: This fall, do you want to see more Doug Joneses elected to the House and Senate?
FLAKE: There are advantages for Republicans to control.
HARWOOD: Have you contemplated post-Senate life? Bob Corker seems to have contemplated it, and decided it doesn't look so good. He's changing his mind.
FLAKE: I haven't changed my mind, no.
HARWOOD: What are you going to do?
FLAKE: I don't know. I'm not swearing off public office. It's just, it's tough for somebody like me in a party like this right now.
HARWOOD: So does that mean we should take seriously the possibility that you might actually run for president?
FLAKE: No, I'm not saying that. I have no plans to run for another office. But I'm not swearing it off. I'll see when it comes.
HARWOOD: Is part of your thinking to preserve your viability politically going forward?
FLAKE: I want to be effective in my final year here. Part of my calculation of leaving, or announcing I was going to leave, is I think somebody needs to speak out who is a sitting senator, who has a forum and a platform to do so. But I'm not going to oppose the president out of spite.