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Trump may not know how obstruction of justice works.

It’s another day in the Trump administration, so the president is stringing together a series of tweets based on friendly Fox News programming about how he has not committed any crimes.

Mixing things up from his usual routine of live-tweeting Fox & Friends, Trump instead provided a kind of greatest hits collection of recent Fox News coverage of his administration. He strikes the familiar notes: that his campaign did not collude with Russia, that he did not obstruct justice as president, that Hillary Clinton is the real criminal, and, of course, WITCH HUNT.

But one point here stands out. Trump quotes Clinton-era special prosecutor Ken Starr saying that Trump did not obstruct justice because, as president, it was completely lawful for him to fire the FBI director. That may be true, but it is also not how obstruction of justice works. Trump absolutely could fire the FBI director for legitimate purposes. But as has been made fairly clear over the past year, the evidence suggesting that James Comey was fired for a legitimate reason is fairly thin, whereas there is a bulk of evidence—including the president’s own statements—suggesting he was fired for the explicit purpose of derailing the Russia investigation. Just because firing the FBI director is legal doesn’t necessarily mean that Trump didn’t commit a crime by firing the FBI director.