The Constitution depends on rivalry and jealousy. It may not be an engine of perpetual conflict, but the separate branches of government and chambers of Congress are supposed to be wary of encroachments on their authority. James Madison hoped that the multitude of interests represented in the legislature would prevent a single will, embodied in a unified majority, from exercising unlimited power.

These are things Americans learn as schoolchildren, but to see the adversarial psychology behind the Constitution play out in today’s impeachment battles is still a shock to behold. President Trump and his White House simply refuse to cooperate with an inquiry opened by a House of Representatives controlled by Democrats. The Republican majority in the Senate looks set to stand by the president, notwithstanding some discomfort and dissent. The Constitution gives the House few powers to punish the president or coerce his compliance.

The public is rapidly becoming acquainted with the reality that impeachment is a political process, not an ordinary legal one. And the portion of the public that most strongly supports the president relishes the fight hardly less than his enemies do.

The defiant letter the White House counsel, Pat Cipollone, addressed to Speaker Nancy Pelosi and Representatives Adam Schiff, Elijah Cummings and Eliot Engel this week was the literary equivalent of one of Mr. Trump’s raucous campaign rallies. It opened several lines of argument against the impeachment inquiry, including the idea that the inquiry’s fundamentally unfair because it doesn’t allow Mr. Trump to challenge accusers and their evidence.

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