NATO spending for Trump was a lot like NATO membership for Ukraine was for Putin... a pretext to follow through on a long-held misguided world view.
I think pushing NATO members to spend more on collective defense is good (Vladimir Vladimirovich has accomplished that more successfully than any POTUS has), but Trump, through his own words and actions, never understood that the money that the United States puts in isn't just giving money away... that we actually benefit from spreading our influence.
My own view is he would have pulled out. And that, as nature abhors a vacuum, others (ie. China) would have stepped in to fill the void. Because, at best, he's an idiot who doesn't understand how American influence works.