From a Washington Post story by Michael S. Rosenwald headlined “A president has never been indicted. But one was arrested.”:

Donald Trump’s claim that he will be arrested imminently has sparked political maneuvering and a debate about the implications of indicting an ex-president.

No president or former president has ever been indicted. But a sitting president was arrested once.

In 1872, President Ulysses S. Grant was arrested at the corner of 13th and M streets NW in Washington. This was not a high crime, but it was — at least theoretically speaking — a misdemeanor.