Facing a tough primary challenge, Sen. Jeff Flake (R-Ariz.) announced his retirement yesterday with a fiery speech on the Senate floor. The speech was striking because it didn't just call out President Trump, labeling his behavior "dangerous to a democracy." He also implicitly called out his colleagues for failing to check Trump. "When we remain silent and fail to act … we dishonor our principles and forsake our obligations," Flake said.

It's hard to argue with this. But it applies equally to Flake himself. He is not "remaining silent" — but that's the easy part. The bigger problem is the failure "to act." If Flake wants his speech to really matter, his words need to be joined by actions.

In his speech, Flake invoked James Madison's famous argument in "Federalist #51" that "[a]mbition must be made to counteract ambition" through the separation of powers. The system of checks and balances has often failed to work the way the framers intended, and the relationship between Trump and the Republican Congress is a case in point. Far from checking Trump's ambitions, congressional Republicans have made an implicit deal, agreeing to overlook Trump's dangerous unfitness for office and unprecedented corruption in exchange for Trump's willingness to advance Republican priorities like upper-class tax cuts, deregulation, and reactionary federal judges.

Flake's speech is not a sign that this devil's bargain is off, precisely because he's no longer seeking office. The fact that Trump's strongest conservative critics are senators — like Flake and Sen. Bob Corker (R-Tenn.) — who aren't intending to seek political office after 2018 illustrates the fundamental problem. As Jonathan Chait of New York puts it, contrary to Madison's expectations "[m]embers of the legislative branch are able to oppose Trump only if they surrender their ambition."

In a sense, then, Flake's pre-emptive retirement represents an initial failure to do what he admonished his colleagues to do and act against Trump. Had he run and defeated his Trumpite primary challenger Kelli Ward, he would have potentially emboldened other Trump skeptics in the Republican conference. And had he lost, the outcome would be the same as retiring. By not even trying to keep his seat, as Dara Lind observes at Vox, "Flake has all but said that you can't have a career in Republican politics while standing up to Trump." His actions, in other words, undercut his words.

So what can Flake do? First of all, he can use his platform as a prominent Trump critic to engage in repeated and specific criticisms of Trump's misbehavior. The media has, for example, mostly stopped talking about Trump's failure to release his tax returns — Flake could draw attention to this. He could also draw attention to Trump's potentially unconstitutional self-dealing and his attempts to disenfranchise voters. If, conversely, Flake's anti-Trump arguments are focused on generalized complaints about his lack of civility, they're unlikely to have much value.

Another action Flake can take is to come out against obviously nutty pro-Trump candidates like Ward and Alabama Republican Senate candidate Roy Moore, who lost his judgeship because he refused to comply with federal court orders and recently declared that the Supreme Court's decision in Obergefell v. Hodges to recognize a national right to same-sex marriage was worse than the Court's determination in Dred Scott v. Sandford that African-Americans were by definition not citizens of the United States. But while Flake has disagreed with some of Moore's comments, he has refused to say that he's unfit to serve in the Senate. If he doesn't think Alabama voters should reject Moore, how serious can his opposition to Trump be?

And, finally, Flake has one very powerful tool: a vote in a Senate in which Republican margins are razor-thin. To his credit, his fellow Arizona senator John McCain hasn't just criticized Trump — he acted to stop a crucial part of his agenda that Senate Majority Leader Mitch McConnell was trying to ram through the Senate using undemocratic methods. Flake, who no longer has to worry about a primary challenge, could tell McConnell that he won't vote for his agenda unless he begins conducting serious oversight of the Trump administration. If he continues to be a reliable vote for Trump's agenda, conversely, his anti-Trump speeches won't mean much.

One could object that it's not realistic to expect a conservative like Flake to vote against Republican policy priorities or to endorse Democratic opponents of even the most Trump-like Republican candidates. Well, maybe, but then Flake can't have it both ways. It's now abundantly clear that a Republican Congress will not check Trump in any way. If tax cuts are more important to Flake than constraining Trump, in the end this makes him no different than McConnell, Paul Ryan, and Trump's other Republican enablers. He's just being a lot more self-righteous about it.