Sen. Jeff Flake’s (R-Ariz.) sudden announcement  Tuesday that he would not seek reelection in 2018 was quickly buried under more remarkable news: A lengthy speech Flake offered from the Senate floor dismissing President Trump and challenging those in his party who, in his words, “accept the daily sundering of our country.” It was a speech about Trump, yes, but it was a speech more broadly about Trumpism and a Republican Party that brought Trump to power and worked against the odds toward his success.

There are natural questions that arise from a move like Flake’s. Why only now is Flake speaking out? Why not fight for his seat and exercise the levers of politics to encourage Arizonans to rebut Trumpism at the ballot box by casting a vote for Jeff Flake? And how can Flake criticize his president and his party when he’s voted with Trump 91.7 percent of the time this year?

More broadly, the critique is this: Why is it only when a senator is retiring that he or she is willing to speak from the heart? And the answer, simply enough, is that it isn’t.

Flake’s move came hours after Sen. Bob Corker (R-Tenn.) criticized Trump more directly and more bluntly. Corker, too, is retiring, which is one reason Flake’s decision not to run was similarly seen as somehow softening his point.

But both Corker and Flake criticized Trump in strong terms well before they announced their retirements. After The Post reported that Trump had revealed classified information in an Oval Office meeting with Russian officials in May, Corker lamented “the chaos that is being created by the lack of discipline — it’s creating an environment that I think makes — it creates a worrisome environment.” In August, before he announced his retirement, Corker said that Trump “has not yet been able to demonstrate the stability, nor some of the competence that he needs to demonstrate in order to be successful.”

For his part, Flake this summer released a book criticizing Trump. Titled “Conscience of a Conservative,” it made a case similar to the one he made  Tuesday. It earned Flake Twitter critiques from the president (comments that Flake on Tuesday derided as containing “the level of thought that goes into 140 characters”).

“Never has a party so quickly or easily abandoned its core principles as my party did in the course of the 2016 campaign,” Flake wrote in the book. Why did it do so? “We did it because it was cheap and easy and the real world is hard and defending a principled position to voters is harder still,” he wrote.

“During the campaign of 2016 . . . committed lifelong free-market conservatives, with their fingers to the wind, took no time at all to dispense with principle and be reborn as ‘fair traders’ or ‘populists.’ All in an effort to chase our own pied piper, who admittedly seemed expert at mapping the nation’s anxieties. Adapting the happy talk of a charismatic outsider was a lot easier than explaining, defending and persuading voters of the things we actually believed.”

Flake never endorsed Trump, even hinting a week before the election that he might back third-party candidate Evan McMullin. When Trump and Flake first met in July of 2016, Flake challenged Trump directly.

Trump said at the meeting that he has yet to attack Flake hard but threatened to begin doing so. Flake stood up to Trump by urging him to stop attacking Mexicans. Trump predicted that Flake would lose his reelection, at which point Flake informed Trump that he was not on the ballot this year, the sources said.

Put another way, Flake was not the sort of Republican that he was calling out in his speech on Tuesday.

Even that 91.7-percent voting record means less than it might seem. It includes a number of bills that any senator might support — like the appointment of Christopher A. Wray to run the FBI. It also includes a number of bills that may have earned Trump’s support but that were squarely in the Republican orthodoxy. It’s also not a terribly high score for a Republican; Sen. John Cornyn (R-Tex.) — to pick someone at random — voted with Trump 96 percent of the time. Flake had the eighth-lowest score among Senate Republicans, according to FiveThirtyEight’s analysis.

The quote above, though, about “defending and persuading voters of the things we actually believed,” seems to be Flake accidentally critiquing his own decision to retire. It’s fair to suggest that a hard-fought campaign on ideas would be a way of demonstrating commitment to those ideals.

That’s easier said than done. Flake faced an uphill climb in his reelection, in part because the electorate in a Republican primary is much more conservative than the electorate in a general election (or even than the Republican voting base generally). Flake was viewed unfavorably by Arizonans and trailed in early primary polling. Flake’s point broadly is that the Republican base had been primed to embrace a Trump-like candidate, making it harder for a Flake-like candidate. It’s a lot to ask a person to spend months and millions of dollars running a campaign to prove a point — especially if the likely result of that campaign is that his ideas and ideals end up on the losing side of the contest.

The critiques of Flake derive to some extent from the same partisanship that’s contributed to so much of the current tension in U.S. politics. A Republican speaking out against Trump can never have done so strongly enough or soon enough for those who oppose Trump’s presidency. For those inclined to such a reaction, though, it’s worth answering one question.

If you want Republicans to criticize the president and those who empower him, which is more important: that the criticism be done in the way you’d like — or that the criticism happen at all?