Being happy about something and supporting something is not the same thing. It is entirely possible that McCain is not happy about Trump but prefers him to the alternative - e.g. splitting the party, losing the election, etc. The world is imperfect, and you don't always get what you're happy about - sometimes you just choose how much of the unhappy you're going to have.
I really don't think that's true.
Do you think John McCain actually supports Trump?
I think the healthy majority of GOP politicians are unhappy with Trump, but saying that is politically dangerous.