Americans often boast that we are a nation of laws, but for the moment laws appear to play a decidedly secondary role in the drama we are living in and—hopefully—through.

We have some guidance from our foundational law, the Constitution, which tells us how to proceed: the House of Representatives has “the sole power of impeachment,” the Senate has “the sole power to try all impeachments,” and must do so “on oath or affirmation.” The Senate cannot convict “without the concurrence of two-thirds of the members present.” And “when...