As far as I can tell, the guy's worldview goes something like this:

A.) In war, lying to the enemy is not only allowable, it's the smart thing to do...
B.) Life is war, and anybody who doesn't let me do anything I want is my enemy...
C.) Anybody who would let me do whatever I want doesn't care if I'm lying or not
... (and while I have no obligation to reciprocate their loyalty, they're useful tools)...
D.) Therefore, I am perfectly justified in lying about anything + everything, anytime
..."Ethics" are for suckers...

I'm not bashing him because he's a Republican president. I got this vibe off of him as far back as the early nineties when he was pretending to be a liberal, because that was what was useful to him at the time, and just about everything he's done or said since then has confirmed it. But you actually have to believe in something (besides yourself) to be a liberal, a conservative, a Nazi, a commie, an anarchist or a theocrat. As the Jewish character Walter in The Big Lebowsi said when confronted by a pack of deranged Nihilists: "Ugh, Nihilists! Say what you will about the tenants of National Socialism, at least it's an Ethos..." (which I don't think was seriously intended as a justification for such an evil philosophy, just another bit of absurd dialogue in that strange little film)
~hugs, Veronica