What did Donald Trump do today?

He suggested stripping Americans of their citizenship as punishment for certain (legal) forms of protest.

Under the Constitution, no natural-born citizen of the United States can ever be stripped of citizenship. Naturalized citizens can only have their citizenships revoked for certain crimes related to the citizenship process, like lying on an application. Trump was talking about flag-burning, which the Supreme Court has upheld as protected speech under the First Amendment. 

How is this a bad thing?

• Making protest a crime and exiling the leader's political opponents is what happens in dictatorships.