From a 21st century vantage point, the idea of impeaching the president for insulting Congress seems odd, to say the least. But as Jeffrey Tulis explained in his seminal work The Rhetorical Presidency, “Johnson’s popular rhetoric violated virtually all of the nineteenth-century norms” surrounding presidential oratory. Johnson stood “as the stark exception to general practice in that century, so demagogic in his appeals to the people” that he resembled “a parody of popular leadership.” The charge, approved by the House but not voted on in the Senate, was controversial at the time, but besides skepticism about whether it reached the level of a high misdemeanor, “the only other argument offered by congressmen in Johnson’s defense was that he was not drunk when giving the speeches.”

It’s impressive that Trump—a teetotaler—manages to pull off his “peculiar indecencies” while stone cold sober. Since his election, Trump has used Twitter to rail against restaurant reviews, Saturday Night Live skits, “so-called judges,” and America’s nuclear-armed rivals. The month before his inauguration, apropos of nothing, Trump announced via the social network that the U.S. “must greatly strengthen and expand its nuclear capability,” following up the next day on Morning Joe with “we will outmatch them at every pass and outlast them all.”

As Charles Fried, Reagan’s solicitor general, observed, “there are no lines for him…no notion of, this is inappropriate, this is indecent, this is unpresidential.” If the standard is “unacceptable risk of injury to the republic,” such behavior just may be impeachable. An impeachment on those grounds wouldn’t just remove a bad president from office; it would set a precedent that might keep future leaders in line.