Clinton v. Jones, decided unanimously as well, also undermines the myth of presidential immunity and undercuts the argument in the Justice Department memos. The court ruled that the president does not have immunity from civil lawsuits — in this case for sexual harassment when Bill Clinton was governor of Arkansas — that arise from private actions unrelated to his official duties as president. The court rejected the argument made by President Clinton’s lawyers that allowing a civil indictment would so badly hinder the functioning of the executive branch that the president should be immune from legal action. The judiciary and the executive branch could work together to “accommodate” the president’s “busy schedule,” the justices said. They also dismissed the argument that their decision would unleash a flood of frivolous lawsuits — an argument now being recycled by Mr. Trump’s lawyers — as mere speculation.

Despite President Trump’s antipathy toward the Clintons, his legal team has drawn heavily from the Clinton Justice Department memo — especially its argument that a criminal trial would render the president too distracted to govern. Of course, the impeachment proceedings he is currently facing are doubtless distracting, but that didn’t stop the framers from including that remedy in the Constitution.

Mr. Trump’s lawyers cite in their defense of absolute immunity the Supreme Court ruling in Nixon v. Fitzgerald, which said the president was entitled to “absolute immunity” from damages in civil suits on matters that pertain to a president’s official duties. But the tax matter before the court involves a criminal investigation, not a lawsuit, and focuses on hush-money payments made to two women just before the 2016 presidential election, when Mr. Trump was a private citizen.

In his brief second inaugural address in 1793, George Washington imagined what should happen were he to disregard his oath of office, saying that “besides incurring constitutional punishment” — presumably a reference to impeachment — he should be “subject to the upbraidings of all” who were witnesses to his swearing-in.

To Washington, the dignity of the office depended on the president respecting constitutional limits. By calling for punishment were he to violate his oath, Washington made clear that the values of the new republic stood above the self-interest of the president. That principle applies in this case too. There is enormous danger to the country when its most powerful official believes he can get away with a crime.

President Trump and his successors must be told in no uncertain terms that they can be held to criminal account if they break the law.

Corey Brettschneider is a political-science professor at Brown and a visiting law professor at Fordham. He is the author of “The Oath and the Office: A Guide to the Constitution for Future Presidents.”