Trump said some things along these lines during his campaign. "I'll be very presidential" comes to mind.
What such pronouncements amount to is a fairly explicit declaration of phoniness. He's quite plainly telling us and everybody that you can't depend on anything he ever says and does.
Jonescu has a short litmus test, that sets a rather low bar, for being able to recognize at least minimal depth in a human being, and says Trump's fails it on all counts:
It was a mistake for the Republican Party to nominate this guy.