SEN. JEFF FLAKE, an Arizona Republican, delivered an address to the U.S. Senate Tuesday that was profoundly eloquent in its diagnosis of the degradation that President Trump has brought to American politics. It was also profoundly depressing. If Republicans can be honest only after they have taken themselves out of the political arena — or if by being honest they disqualify themselves from future service — then their party and therefore the nation are in even graver trouble than we knew.

Mr. Flake had intended to run for reelection next year. But a book he published that criticized Mr. Trump made him vulnerable to a primary challenge. "It is clear at this moment that a traditional conservative who believes in limited government and free markets, who is devoted to free trade, and who is pro-immigration has a narrower and narrower path to nomination in the Republican Party," Mr. Flake said Tuesday. " It is also clear to me for the moment we have given in or given up on those core principles in favor of the more viscerally satisfying anger and resentment."

So Mr. Flake will not run in 2018 — and, liberated from political necessity, he offered a cogent lament for the state of the union: "We must never meekly accept the daily sundering of our country — the personal attacks, the threats against principles, freedoms, and institutions; the flagrant disregard for truth or decency, the reckless provocations, most often for the pettiest and most personal reasons. . . . And when such behavior emanates from the top of our government, it is something else: It is dangerous to a democracy."

"None of this is normal," Mr. Flake said. "And what do we as United States senators have to say about it?"

The answer: not much. Bob Corker (R-Tenn.) has been speaking up — after he, too, decided not to stand for reelection. A few others have shown some courage at times: Mr. Flake's fellow Arizonan, the indomitable John McCain; the independent- ­minded Susan Collins of Maine; Alaska's Lisa Murkowski. But given that Mr. Flake's fellow Republicans privately agree with much of what he had to say, the silence from his leaders and most of his colleagues is overpowering.

Will they be emboldened by Mr. Flake's candor — or chastened by his example? We fear the latter is more likely. Republicans who fancy themselves true conservatives, such as Mr. Flake, should stand up against Mr. Trump's noxious politics, as the senator implored on Tuesday. But they have to do more than that. They have to fashion an agenda and a political style that can compete successfully in primaries against Trumpism. Until they do, all the eloquence in the world will not be enough.