Even worse is a provision that would let Mr. Mueller appeal his dismissal to a federal judge. Making Article III judges arbiters of the President’s appointment power undermines the separation of powers and dilutes political accountability. There is no such judicial power in the Constitution unless a President acts unlawfully, and firing Mr. Mueller would be a political mistake but it wouldn’t be unlawful.

Perhaps Mr. Flake, who didn’t run for re-election, is making a political statement in advance of the primary run he says he may make against Mr. Trump in 2020 in New Hampshire. But Republicans are likely to notice that he put his personal feelings about Mr. Trump above confirming judges that any GOP President would be proud to nominate.

Recall that John McCain scuttled the Republican effort to repeal ObamaCare, in part because of his personal distaste for the President. But in the long run he will have harmed the institution he spent his career trying to protect: the military, which is squeezed by unreformed health-care entitlements. Mr. Flake’s self-indulgence is another example of how hostility to Mr. Trump has caused so many people to lose their own political bearings.