What did Donald Trump do today?

Witness tampering.

Trump spent most of the morning on Twitter. He called for one potential witness against him, former "fixer" and Trump Organization vice-president Michael Cohen, to "serve a full and complete sentence." Then he lavished praise on another potential witness, Roger Stone, for having the "guts" not to cooperate with the Russia investigation.

As both Republican and Democratic lawyers immediately pointed out, this is textbook witness tampering, which is a federal crime. 

Specifically, it is a crime to use intimidation to cause a witness to refrain from offering testimony—for example, by publicly saying as the head of the executive branch that federal prosecutors under your employ should seek a "full and complete" sentence for defendants who would testify against you.

It is also a crime to "corruptly persuade" the testimony of a witness—especially in the context of a broader campaign to influence potential witnesses by hinting at leniency or pardons. Trump has pointedly refused to publicly rule out pardoning co-conspirators who could testify against him.

Trump also made the odd claim that Cohen was being prosecuted for crimes "unrelated to Trump." They are not.

Why should I care about this?

• Innocent people don't generally try to threaten or sweet-talk witnesses.

• Presidents are not above the law.

• A president who doesn't want special counsels using anti-Mafia tactics against him shouldn't behave like a Mafia boss.