David A. Graham: The whistle-blower’s explosive allegations

That standoff was ultimately resolved in Congress’s favor. Nixon turned over the tapes, and soon after resigned. Legal experts expect that Trump would fare no better in the courts—he hasn’t this week—but he may hope to stall investigations until it’s too late for Democrats to do anything. It’s a strategy that’s worked for him before.

Even before Cipollone’s letter, constitutional experts said Trump’s attempts at stonewalling were baseless.

“He doesn’t have any power to do this. It’s just a flat defiance of an obvious congressional authority,” Frank Bowman III, a professor of law at the University of Missouri and the author of a recent book on impeachment, told me. “The House has the power to inquire into facts that would support an impeachment. The president simply has no authority to refuse to produce those facts.”

Michael Gerhardt, a law professor at the University of North Carolina and a nationally recognized expert on impeachment, agrees that Trump had no grounds for blocking testimony. “He is playing politics and nothing but politics, though the law is clear: No privilege precludes an ambassador or any other official from talking about legal violations and abuse of power,” Gerhardt said in an email.

Indeed, though the letter is signed by the White House’s top lawyer, its arguments are predominantly political rather than legal. In the first section of the letter, Cipollone lays out a few arguments based in law. He notes that the House has not held a vote to officially open an impeachment inquiry, which is true but largely beside the point; there’s no legal requirement to hold a vote at this stage. Cipollone also complains that Trump has not been given sufficient opportunity to defend himself or respond to charges, and that this violates due process.

The problem for Trump is that the Constitution is minimal but direct on the matter of impeachment, leaving the rules to the House to set. If the House were to vote to impeach Trump without offering him a chance to defend himself, it would raise political questions of fairness—but the House is only in a fact-gathering stage, trying to interview witnesses and collect information, and hasn’t even drafted articles of impeachment, which would come to a vote.

David A. Graham: Trump is panicking

Cipollone argues that House Republicans should have subpoena power, saying that minority parties had that power during the Nixon and Bill Clinton impeachments—but in both cases, minority subpoenas would have been subject to a vote by full committee, giving the majority a de facto veto.

Finally, the letter argues that executive privilege allows Trump to prevent testimony. But as Bowman noted, Nixon v. United States concluded that the president can’t invoke executive privilege to withhold evidence in a criminal case—a precedent that would probably apply to impeachment as well. “It’s clear as such a thing can be that a president cannot exercise executive privilege to bar the House from getting information necessary to exercise its impeachment power,” he said.