In 1973, I worked as a lawyer on Cox’s task force investigating obstruction-of-justice allegations against Nixon. The White House tapes show that, by the summer of 1973, the president had grown increasingly frustrated over Cox’s examination of alleged misconduct, which included a conspiracy to obstruct justice by the president’s closest aides. Cox’s dogged pursuit of nine specific tape recordings was the last straw. The special prosecutor wanted the audio for a reason: Ever since White House Staff Secretary Alexander Butterfield had revealed the existence of Nixon’s voice-activated taping system, in July 1973, Cox hoped to use the recordings to resolve disputed facts about who said what in conversations with the president.

Yet Nixon refused to turn them over—even after he was subpoenaed by a grand jury and under orders from two separate courts. Instead, the president proposed that Cox accept the compromise, under which he would receive summaries of the taped conversations prepared by Nixon. Cox’s refusal to agree to any substitute for the tapes themselves provided Nixon the pretext he was seeking to remove the special prosecutor, and to return the investigation to more pliant personnel within the Justice Department.

The nation correctly perceived that Nixon’s true intention was to prevent Cox from uncovering evidence of criminal misconduct that Nixon was determined to keep hidden. While Trump’s true intentions remain unknown, his feelings about Mueller, at least, are crystal clear—he hasn’t tried to hide them. In multiple public statements, he and his associates have condemned Mueller’s investigation, and one of his lawyers went so far as to say the inquiry should be shut down.

As with Cox, Mueller and his staff have done nothing publicly known that would provide a legitimate reason to justify dismissal: They do not appear to be the source of leaks to news media, nor have they committed any known improprieties. Instead, Mueller has been methodically investigating under the mandate he was given and is building out cases in multiple directions.

Trump seems to have reached breaking points with Mueller before. In June, he reportedly instructed White House Counsel Don McGahn to orchestrate Mueller’s firing, only to back off when McGahn threatened to resign. On Tuesday, The New York Times reported that a similar episode happened in December, when the president erupted in anger over an erroneous news article wrongly attributing certain subpoenas of financial documents to Mueller’s probe. Again, Trump’s immediate impulse was to fire Mueller, according to the Times.

There’s nothing to suggest Trump has changed his mind about the Mueller inquiry in the months since. To the contrary, Trump raged this week over investigators’ latest target: Michael Cohen, a New York lawyer who’s long functioned as the president’s fixer and who allegedly paid off women who claim they had affairs with Trump. Hours after the FBI raided Cohen’s home, office, and hotel room, Trump called the Mueller probe a “disgrace” in comments to reporters, telling them that “many people have said, ‘You should fire him.’”