Have you ever read what the Constitution says about the duties of the President? Article 2. Section 2. It would almost make you laugh when you see what a monarch/caesar/king position we have today if it weren't so pathetic. I think there may be more words spent on the electoral system (Section 1). The gist is, his primary job is to be Commander in Chief of the army and navy, but he can also grant pardons, appoint ambassadors, judges, etc. (with consent of the Senate) and he...'s supposed to give a state of the union message from time to time. And although everyone says we have three equal branches, it's pretty clear on reading it, (Article 1, the longest part of the Constitution) that Congress was to be the power house, especially the House of Representatives, because that's how we the people were to have a voice, a voice no one in Europe had at that time.
By deduction, I'm guessing the Founders meant the President's primary job was to keep the nation safe. Given his awful, blame-game, finger pointing speech yesterday, calling for more gun control and chastising those who won't give it to him, I'd say he knows what his real job is, but he has to pretend it's not his fault that ISIS has taken center stage in the world and grown in power and become a threat here under his management. He refuses to say, the buck stops here, like Harry Truman. He hasn't kept us safe and he won't or can't.