Congress has approved legislation that would prevent any president from withdrawing the United States from NATO without approval from the Senate or an Act of Congress. The measure, spearheade…
The fact that this is even something Congress needed to consider doing is crazy.
The main purpose of the US military is deterrence. Soldiers and tanks and aircraft carriers do their job by being so intimidating that no one starts a major war. (They're still useful if a war does start, but winning a war is far worse than not having to fight it in the first place.) A major component of this system of deterrence is the presentation of an indivisible united front between us and our allies. Simply having the President publicly question the dedication of the USA to NATO did billions of dollars worth of damage - compare how much better it would be to have had Trump keep his mouth shut than it would be to build an extra carrier battle group. (Arguments about who pays how much can be held in secret.)
The fun part is that they can pass a law to prevent Trump from officially leaving NATO, but they can't pass a law to make him actually honor the alliance if a war does start, and they especially can't pass a law to make the enemies of the USA believe that he would honor the alliance.