Joshua Roberts / Reuters

There’s no use in pretending that the White House’s announcement that it has directed former White House Counsel Don McGahn not to testify to Congress comes as a surprise.

It is only the latest salvo in the skirmish between Donald Trump’s administration and the Democratic House. The White House had already told McGahn not to supply documents to the House Judiciary Committee under subpoena. It sued to prevent the president’s accounting firm from providing documents to the House Oversight Committee. Treasury Secretary Steven Mnuchin has refused to comply with a House Ways and Means subpoena for President Trump’s tax returns. Attorney General William Barr has been held in contempt for refusing to testify to the House Judiciary Committee. Faced with Democratic investigations, the Trump team has settled on a strategy of foot-dragging and dubious legal theories.

Yet while the McGahn contretemps was predictable, it’s arguably more important than any of the other tugs of war between the House and White House. More than that of any other witness, McGahn’s testimony would deal directly with whether and how Trump obstructed justice—and it would come closest to showing what an impeachment proceeding against Trump would look like.

In support of the direction to McGahn, the administration released a legal rationale developed by the Office of Legal Counsel. It’s impossible to say whether it will hold up in court. In broad strokes, it seems like a somewhat novel assertion, and a broader one than what previous administrations have claimed. However, the test will come in a courtroom, or several, and this Supreme Court has proved sympathetic to assertions of executive power. The OLC opinion does not, as Zoe Tillman and Steve Vladeck note, actually block McGahn from testifying, or claim that the president can. Instead, it says that he isn’t legally required to do so.

But McGahn has plenty of reasons he might not want to show up. It’s hard to see how he would benefit from testifying, and whatever Democrats hope to get out of McGahn as ammo against the president, they would surely have some tough questions for McGahn as well. Testimony would probably bring unwanted flak from Trump, and it would bring unwanted attention on McGahn’s law firm, Jones Day, which does a lot of work for Republican politicians. (The Trump campaign used to be a client, but in April it hired an in-house lawyer, in what was interpreted by some as a swipe at McGahn.)

The White House also has plenty of reasons it wouldn’t want McGahn to show up, too. There’s been lots of attention given to the prospect of Barr or Special Counsel Robert Mueller testifying to the House. “Frustrated House Democrats Pin Their Hopes on Mueller,” The New York Times announced last week. What Democrats imagine they’re going to get out of either man testifying is unclear. Consider Barr’s testimony to the Senate Judiciary Committee on May 1. The attorney general occasionally made some missteps, and it was a useful forum for Senator Kamala Harris to boost her presidential campaign. It did not, however, produce any epiphanies, and no surprise—Barr, on his second tour as attorney general, knows how to deflect.

It’s been nearly two months since Mueller submitted his report, and despite Democrats saying since then that they want to hear from him, there’s still no testimony scheduled, because Mueller has not agreed to testify yet. Unlike Barr, Mueller has not dedicated himself to Trump’s devoted defense, but he’s unlikely to be all that interesting, either. Mueller had 448 pages in which to express his views, and if he wanted to accuse the president of obstruction of justice, that’s where he would have done it.

Moreover, Mueller and Barr are each at least a degree removed from the action: Mueller investigated the underlying events, and Barr summarized and redacted Mueller’s report. Each man has already made his view clear. While Mueller could speak to his disagreement with Barr over summarizing his report, that report strongly implies that Congress ought to do the deciding on obstruction, and he’s unlikely to be especially patient if it tries to bounce the decision back to him.

But McGahn was an eyewitness to, and often a participant in, the events described. Trump says that he never actually told McGahn to fire Mueller, contrary to the Mueller report. So why did McGahn think that? The best person to answer that is Don McGahn. Why did McGahn feel his job was being threatened? Barr and Mueller can only speculate, but McGahn actually knows. Why did McGahn decline to write a letter saying Trump didn’t obstruct justice? McGahn is the man to answer. With collusion receding from view and obstruction taking center stage, McGahn is more central than any possible witness except Trump.

On Monday evening, The Washington Post reported that Michael Cohen, Trump’s former personal attorney for the president, alleged to Congress that Jay Sekulow, a current personal attorney for the president, had instructed him to lie about when negotiations over a possible Trump Tower Moscow ended. That’s yet another reason Congress would want to hear directly from the former White House counsel on whether Trump tried to use a lawyer to obstruct justice.

Not only would McGahn be far more likely to provide Congress and the public with new information, but this very fact would also make the proceeding resemble an impeachment hearing—an outcome that Speaker Nancy Pelosi and Judiciary Committee Chair Jerry Nadler have sought to forestall, or at least slow. If the House moved forward on impeachment, it would want testimony from participants in the events themselves, not other people or groups who have already conducted their own investigations. Testimony from a White House counsel can be devastating to a president—just ask John Dean.

This would make McGahn’s testimony, far more than Barr’s or Mueller’s, the main event in House investigations into the Trump administration. That means that among the several fights over executive privilege between the White House and House, this one is at the top of the card.

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