By failing to take any action to stop the violence at the Capitol on Jan. 6, may have violated 18 USC § 1505 - Obstruction of proceedings before departments, agencies, and committees
18 USC § 1505 - Obstruction of proceedings before departments, agencies, and committees
Whoever corruptly, or by threats or force, or by any threatening letter or communication influences, obstructs, or impedes or endeavors to influence, obstruct, or impede the due and proper administration of the law under which any pending proceeding is being had before any department or agency of the United States, or the due and proper exercise of the power of inquiry under which any inquiry or investigation is being had by either House, or any committee of either House or any joint committee of the Congress—
This is the exact law that most of the 1/6 insurrectionists themselves have been charged with. Their lawyers have repeatedly challenged the application of this law to their clients, but so far, five separate federal judges have ruled that those charges are viable.
By failing to take action when he had the power to do so, Trump violated both this law, and his Oath of Office, which means he also violated the US Constitution.
While there is no Federal code or punishment for the latter, it is subject to the 14th Amendment, and someone who has failed to uphold their Oath of Office could be disqualified from ever holding office again.