Will Baude has some interesting thoughts on presidential fidelity to the law that relate to my Scofflaw Principle. I think I come down with theory #3:
Government officials are special. Civilians may have no moral obligation to obey the law (see #1), but government officials are empowered by the law, so they are specially obligated to take the bitter with the sweet. The oath of office operates to convert law into a personal promise.
By government officials, I mean specifically executive-branch officials, in regard to the law they are tasked with administering. For the president that’s everything (or, more precisely, all Constitutional federal law). For other executive-branch officials it depends on their portfolio: if you work at the IRS, you might not be morally obliged to obey speed limits, but you had better obey every jot and tittle of tax law.