Trump’s opposition to Mueller testimony poses a test for Barr

But that solution to Mr. Barr’s dilemma is fragile.

It would collapse if Mr. Trump, who tweeted his objection to Mr. Mueller’s potential testimony over the weekend, were to decide to press the issue by explicitly ordering Mr. Barr to gag the special counsel. Mr. Barr’s handling of the Mueller report so far has prompted critics to accuse him of acting more like the president’s lawyer than an honest broker.

But if Mr. Barr ignores Mr. Trump’s statement because it fell short of a formal and direct order, that would be the behavior of an attorney general who sees his client more as the presidency as an institution than Mr. Trump, said Harold Bruff, a University of Colorado emeritus law professor and co-author of a separation-of-powers casebook.

“Who is his client?” Mr. Bruff said. “Is his client the person who is the president? If so, then the merest suggestion is as close to an order as you need. It’s a little like being married.”