Senate Republicans are taking even more media abuse than usual after voting to bar witnesses from the impeachment trial of President Trump. “Cringing abdication” and “a dishonorable Senate” are two examples of the sputtering progressive rage. On the contrary, we think it was Lamar Alexander’s finest hour.

The Tennessee Republican, who isn’t running for re-election this year, was a decisive vote in the narrowly divided Senate on calling witnesses. He listened to the evidence and arguments from both sides, and then he offered...