The president of the United States is lying again.

He is lying about the reason he fired James Comey, the F.B.I. director. Trump claimed that he was doing so because Comey bungled the investigation into Hillary Clinton’s email, which meant that Comey was “not able to effectively lead the bureau.”

There is no reason to believe Trump’s version of the facts and many reasons to believe he is lying. How can I be so confident?

First, it’s important to remember just how often Trump lies. Virtually whenever he finds it more convenient to tell a falsehood than to tell a truth, he chooses the falsehood.

An incomplete list of the things he has lied about include: Barack Obama’s birthplace, Obama’s phone “tapp,” John F. Kennedy’s assassination, Sept. 11, the Iraq war, ISIS, NATO, military veterans, Mexican immigrants, Muslim immigrants, anti-Semitic attacks, the unemployment rate, the murder rate, the Electoral College, voter fraud, the size of his inaugural crowd, his health care bill and his own groping of women.