In seeking to join suit over subpoena power, Mulvaney goes up against the president

In effect, Mr. Mulvaney hopes the court will tell him whether to listen to his own boss, who wants him to remain silent, or to comply with a subpoena from the House, which wants his testimony. That put Mr. Mulvaney at odds with some other current White House and administration officials who had simply defied the House, citing the president’s order not to cooperate with what he called an illegitimate “witch hunt.”

Mr. Mulvaney did not explain why he chose a different course, but his decision focused renewed attention on his relationship with Mr. Trump; it has been increasingly strained as House Democrats prepare to open public hearings into whether the president should be impeached for high crimes and misdemeanors.

“It’s symptomatic of a White House that is more dysfunctional than ever — except now it’s not just chaos, the long knives are coming out,” said Chris Whipple, the author of “The Gatekeepers,” a history of White House chiefs of staff. “Everybody, including the White House chief, seems to be lawyering up.”

Mr. Whipple could not think of any precedent for a chief of staff going to court rather than obey a president’s order.