> The president is not constitutionally incapable of committing crimes
I doubt the president will ever be arrested or tried in a traditional court while holding office. If the president was literally murdering people in public, Congress would have to have an emergency session, impeach the president, remove the president from office, then there'd probably be a trial somewhere that got appealed all the way up to the Supreme Court to decide if it was a valid trial.
"The Constitution does not answer every question. It includes detailed instructions, for instance, about how Congress may remove a president who has committed serious offenses. But it does not say whether the president may be criminally prosecuted in the meantime."
https://www.nytimes.com/2017/05/29/us/politics/a-constitutio...
> So, yes, Presidents can definitely break the law, including laws that have to do with speech.
There's a legal theory that the president, while serving the duties of the office, is given certain immunities. This is why the president doesn't always respond to subpoenas and why the local government can't issue a search warrant for Air Force One, etc.
caveat: I am not a lawyer, though from my reading this isn't a matter of settled law anyway, so even lawyers are speculating.