Ken Gormley is president of Duquesne University and author of "The Presidents and the Constitution: A Living History."

President Trump owes his White House counsel a thank-you note. Here is the paradoxical reason: The best way for Trump to protect himself against special counsel Robert S. Mueller III is not to fire him.

That is one of the essential lessons of Watergate: It was only after President Richard Nixon fired Watergate special prosecutor Archibald Cox that a firestorm of public protest erupted, resulting in the eventual unraveling of the Nixon presidency.

There's little doubt Trump could find a way to engineer Mueller's departure. As Cox told reporters just hours before Nixon fired him, "Eventually, a president can always work his will."

But what happened after Cox's ouster is instructive. President Trump should keep in mind: Removing a special counsel does not extinguish an ongoing investigation. Immediately after Cox was fired, his entire special prosecution team reported to work in a show of solidarity. Public outrage at Nixon's action empowered the second appointed special prosecutor, Leon Jaworski, who subpoenaed even more Watergate-related White House tapes, causing Nixon to fly away in a green helicopter in disgrace.

What Trump's lawyers should advise their client is that he's better off gritting his teeth and allowing the Mueller investigation to run its course instead of sticking his hand into a constitutional bear trap. If he can do this, the Constitution will shift the equation strongly in his favor, no matter the result of Mueller's investigation.

This broader legal picture is often overlooked: Most constitutional experts agree that a sitting president cannot be indicted and prosecuted while in office; any criminal prosecution must await the president's departure — or removal — from the White House. In Federalist No. 69, Alexander Hamilton said a president could be impeached and removed from office "and would afterwards be liable to prosecution and punishment."

The framers required impeachment before criminal prosecution for good reason. As the unitary head of the executive branch, the president is unlike any other official in our system. If a president were to be prosecuted while in office, arrest and jail could follow, which would paralyze the entire executive branch of government.

Thus, Trump's firewall against a politically motivated prosecution by Mueller or anyone else is Article 1 of the Constitution. He cannot be touched while in office, unless a majority of the House and two-thirds of the Senate (both controlled by his own party) determine he is guilty of an impeachable offense. This is an extraordinarily high hurdle. It's why President Andrew Johnson was able to finish his term and President Bill Clinton did not come close to being removed. It would take a smoking gun — a blockbuster piece of evidence such as the damning White House tapes in Watergate — to overcome the strong protections built into the Constitution and put the president in political jeopardy.

Even if Mueller's investigation unearthed crimes by Trump's campaign staff or others working for him, it's hard to imagine how this alone would rise to the level of an impeachable offense. Moreover, the Constitution provides that the Supreme Court's chief justice — now Republican appointee John G. Roberts Jr. — would preside over any Senate trial, further diminishing the chances of partisan mischief. Any charges that contain even a whiff of partisan politics would be dead on arrival.

Once Mueller issues a report, takes steps to ensure that it gets into the hands of Congress (if he sees any potential grounds for impeachment) and wraps up any remaining criminal matters, there's no reason for him to stay in business. Any criminal action against Trump himself would be frozen in place; it would have to await his leaving office in 2021 or 2025, at which point there would be ample leverage for Trump's lawyers to strike a deal with the Justice Department (as Clinton did when he moved out of the White House). An outgoing president — let alone one nearing 80 years of age — is hardly a prime target for criminal action.

No president likes to be investigated by special prosecutors. President Ronald Reagan bristled at the Iran-contra probe. His successor, President George H.W. Bush, called it "profoundly troubling" and pardoned key defendants. Clinton described the Whitewater investigation that morphed into the Paula Jones and Monica Lewinsky sagas as an ideologically driven crusade, a "Stalinist show trial" and a failed coup d'état.

Yet strong presidents learn to live with such unpleasantness so they are not eaten alive by it. Weathering a special prosecutor's investigation is like enduring an intrusive, undignified medical examination. It's no picnic. But refusing to let it go forward presents much bigger problems for the chief executive and for the whole country that must deal with the consequences.