The verb to lynch means to execute without a trial or due process. It doesn’t refer only to extrajudicial killings in the post-Reconstruction and Jim Crow South. Accordingly, it’s occasionally used in a figurative sense in other English-speaking countries. But in the United States the word is electric for its historical context, and you don’t have to indulge in racial hypersensitivities to appreciate why. Clarence Thomas famously used it during his confirmation hearing in 1991 when, as he saw it, a cabal of white liberals sought to destroy his nomination to the Supreme Court by a “high-tech lynching.” Justice Thomas had what we would call political and historical standing.

But no President should use the word in the off-hand and self-indulgent way that Mr. Trump did in his tweet. What’s so galling about this and similar pointless provocations is that, in his quest to remain always and forever in the headlines, Mr. Trump puts his more judicious allies on the political spot. Every Republican in Congress is immediately asked either to ignore him and risk association with his reckless pronouncements, or criticize him and risk his wrath.