In all three of those precedents, the appointment of special or independent prosecutors and their subsequent investigations took years to bear results, especially with respect to the president. None of those investigations was particularly disruptive until a credible threat of impeachment materialized. And, most importantly for Trump, none of the investigations on their own significantly eroded intra-party support for the president.

If these precedents are a reliable guide, Trump ought to benefit from the two-way street that runs between congressional backing (needed to stave off impeachment) and popular support within the party (needed to discourage congressmen from abandoning ship). Based on timing alone, the key to his fate will likely be the 2018 midterm elections, not the special counsel. If Democrats take back the House—and regain the power to issue subpoenas and hold public hearings—Trump will be in real trouble.

Start with timing. Republican members of Congress are praying a smoking gun does not emerge to damage their party’s president in the 14 months between now and the midterms. On this count, they may be in luck. “Saturday Night Massacre” aside, the Watergate special investigation took 14 months before it reached a fever pitch with the Supreme Court’s ruling that Nixon was required to turn over the White House tapes. And although Nixon resigned shortly thereafter, in August 1974, the investigation itself ran until 1977.

That case was the speediest of the three. Iran-Contra Independent Counsel Lawrence Walsh was appointed in December 1986, first indicted senior officials in 1988, and did not publish his final report until 1993. Kenneth Starr’s tenure as independent counsel is notorious for its protracted timeline, running from January 1994 to September 1998. Given the sensitivity of his remit, Mueller will likely be in no rush to produce findings with anything less than certainty. If he follows his predecessors’ timelines, that could take a while.Perhaps the most critical variable for Trump, though, is popular support among Republican voters. Their favor holds the key to keeping anxious Republican lawmakers’ fingers off the impeachment trigger and this embattled administration in business. Here, too, the precedents suggest little for Trump to worry about in the near term. Of the three presidents who have faced similar investigations, only Nixon saw a catastrophic loss of partisan support.

Nixon’s loss of popular support, however, was not due to the appointment of a special prosecutor or the results of his investigation. Nixon saw two notable declines in Republican approval during the Watergate investigation: one in January 1973, when two campaign aides were convicted in connection with the Watergate burglary (unrelated to the special prosecutor’s investigation), and another during the summer of the same year, at the height of nationally televised Senate hearings into the matter (when his support was already beginning to erode).