Update (7:29PM): Given that these events occurred on federal property, maybe it should be the FBI making the arrest under this law, and the United States Attorney for the District of Columbia, Michael R. Sherwin, should be the one to bring charges.
Update #3 (7 Jan.): First Amendment scholar Eugene Volokh (UCLA) takes an opposing view. Alas, Professor Volokh’s narrow reading of the leading incitement case, Brandenburg v. Ohio, is open to debate. President Trump’s incendiary speech, just minutes before the attack on Capitol Hill, was like yelling fire in a crowded theater!
Update #4 (8 Jan.): According to this report via CNBC, the federal prosecutor for DC has not ruled out charging President Trump for incitement!
Update #5 (10 Jan.): Senator Pat Toomey agrees with me that Trump might incur criminal liability for the 6 January Coup Attempt. #RuleOfLaw