Well, of course he will. Who will try to stop him? Via the New York Times:
For nearly four years, President Trump has publicly railed against the North Atlantic Treaty Organization, angrily demanding that its members pay more for Europe’s collective defense. In private, Mr. Trump has gone further — speaking repeatedly about withdrawing altogether from the 71-year-old military alliance, according to those familiar with the conversations.
In a second term, he may get his chance.
Recent accounts by former senior national security officials in the Trump administration have contributed to growing unease on Capitol Hill and across Europe. They lend credence to a scenario in which Mr. Trump, emboldened by re-election and potentially surrounded by an inexperienced second-term national security team, could finally move to undermine — or even end — the United States’ NATO membership.
These former officials warn that such a move would be one of the biggest global strategic shifts in generations and a major victory for President Vladimir V. Putin of Russia.
John Bolton's book talked about it. So did Michael Schmidt's, in which he recounted John Kelly saying “one of the most difficult tasks he faced with Trump was trying to stop him from pulling out of NATO.”
But really, I can see him doing it because NATO leaders made fun of him. He always wants to get even. And this sounds a lot like something Trump would do:
Congress would most likely move to block any effort by Mr. Trump to exit the alliance altogether, but experts said he could deal it a near-lethal blow in other ways. One would be to undermine a provision in the original treaty, Article 5, that calls for collective self-defense. Previous presidents have interpreted it as a promise to defend any member from military attacks, but Mr. Trump has questioned it.
“He could just reinterpret it as, ‘I could just send a strongly worded letter,’” Mr. Wright said.