Damn right you aren't. Your oath is towards the constitution, not any single person. And you not only have a right to not obey unlawful orders, you have a solemn duty to defy them. Any dictator only has as much power as his enforcing branch - the military - will allow him. Take the military away, and they're just overgrown children throwing a tantrum, subject to the will of the common people.
This has been said to death, but "I was following orders" was not a valid justification in Nuremberg, and it will be even less so this time around.