The White House letter late Tuesday telling Speaker Nancy Pelosi that President Trump won’t cooperate with her impeachment inquiry is causing heartburn among all the usual suspects. Readers should ignore the fainting spells over “a constitutional crisis” and keep in mind that this is largely a political response to a political attack by House Democrats.

“Your inquiry is constitutionally invalid and a violation of due process,” wrote White House counsel Pat Cipollone, who lists the due-process protections that the House is...