It’s in his “agreement” isn’t it? Oh, wait, he screwed up the presidential oath at the inauguration and had to do it over again....behind closed doors. God knows what he swore to.
Nope it's not, even if he'd recited it correctly.
Before he enter on the Execution of his Office, he shall take the following Oath or Affirmation: — "I do solemnly swear (or affirm) that I will faithfully execute the Office of President of the United States, and will to the best of my Ability, preserve, protect and defend the Constitution of the United States."
You can read of Article II of the Constitution, there's nothing in there about the President being obliged to defend the country, although the tools to do so are placed into his hands there.