What did Donald Trump do today?

He channeled Richard Nixon on presidential criminal law.

In a Saturday tweet, Trump appeared to confess that he had obstructed justice when he admitted that he knew at the time of his firing that Michael Flynn had lied to the FBI. That makes his subsequent efforts to shut down the investigation into Flynn--which culminated in the firing of the FBI director, James Comey--obstruction on its face.

Today, Trump's personal defense lawyer John Dowd offered a new sort of defense: not that Trump didn't or wouldn't seek to pervert the course of justice by firing Comey over his pursuit of legitimate crimes, but that as president, nothing Trump does can ever legally count as obstruction of justice. Dowd told Axios.com that a "president cannot obstruct justice because he is the chief law enforcement officer under [the Constitution's Article II] and has every right to express his view of any case."

This is not an entirely new theory: President Nixon made the same argument, although only after he'd left office and accepted a pardon for crimes he'd committed while in office.

FROST: Would you say that there are certain situations... where the president can decide that it's in the best interests of the nation, and do something illegal?

NIXON: Well, when the president does it, that means that it is not illegal.

Trump's legal theory didn't impress most lawyers asked for comment today, but since Trump probably can't be criminally indicted until after he leaves or is removed from office, it may be a moot point. That said, obstruction of justice was a charge against President Clinton during his impeachment trial and an article voted out of committee against President Nixon, who resigned rather than be impeached.

Why does this matter?

• It's bad if a president perverts the course of justice, whether or not he can be prosecuted for it.

• Declaring yourself above the rule of law is what authoritarians do.