The last-minute addition of a repeal of Obamacare’s individual mandate and the various accounting gimmicks built into the bill aren’t there so that tax reform doesn’t add to deficits. They’re there so that it doesn’t add to deficits by more than $1.5 trillion over 10 years. You can’t support this legislation and call yourself a deficit hawk. More like a deficit ostrich.

That should be reason enough for Senator Bob Corker, the Tennessee Republican, to vote no. What’s more, he has also denounced Trump as “an utterly untruthful president” who needs “adult day care” and is “unable to rise to the occasion.” Does Corker want to march in lock step with such a disaster or trip him up?

That same question goes to John McCain, to Susan Collins and to other Senate Republicans who have indicated grave apprehensions about Trump. Their party’s donors may be demanding tax reform. They themselves may believe in some of the bill’s particulars. But do they believe in this president? In where he has tugged the G.O.P.? Do they want to aid him, or put him behind them as quickly as possible?

Some Republicans beyond Trump would be hurt by a defeat on tax reform. But they’d be hurt more in the long run by sustained surrender to him. To crib a phrase from Flake, they’d be toast.

In his book “Conscience of a Conservative,” which was published in August and was the prelude to his big speech, Flake wrote that Republicans indulged Trump by rationalizing that he might help them “achieve some long-held policy goals.” But Flake added that if this “put at risk our institutions and our values,” it raised the question of “whether any such policy victories wouldn’t be Pyrrhic ones.”

That question is no less pertinent now. Trump continues, on an almost daily basis, to dishonor the presidency and debase civic life. We may be getting more used to him; he’s not getting any better. He picks gratuitous fights — with the widow of a slain soldier, with the father of a detained college basketball player. He curtsies to the Russians and the Chinese. He petrifies his own inner circle. His secretary of state supposedly called him a “moron.” His national security adviser reportedly opted for “idiot” and “dope.”

Flake’s message a month ago had a more elevated vocabulary but the same urgency. He said that lawmakers must be “unafraid to stand up and speak out as if our country depends on it, because it does.” Was that preening or patriotism? He can show us with a single vote.