I don't think that Trump supports the dissolution of NATO. What he wants is more contribution from the EU nations. US spends close to $600 billion every year on defense purposes, while the military budget of nations such as Germany and England remains as a small percentage if their national GDP. Trump wants the EU nations to contribute in terms of funds, equipment and manpower. And I don't think that there is anything wrong in what he says. Why should the US subsidize the national defense of EU nations? Doesn't make any sense.
There is also a good way of saying "we just won't spend this much on military anymore" and the left would be all behind that, would Trump do that? Or is he just want more for the people who bribed him to be there?
If you spend 800 billion on military and lets say that 100 of that goes to spending on NATO, would you cut it to 700 and not help NATO, or would you keep it at 800 and spend it on Warhawk companies in the USA? That's the real question, if we are talking about a cut, which Trump could have done any time in his 4 year tenure, that would be fine and accepted by everyone, this is why it would be a lot better if we just knew what he would do by his first 4 years, if he didn't then nobody would trust him to do it in another 4 years, could be a big lie.