The US leaving NATO would be a huge blessing to Global World Peace. Nobody wants US imperialism, guised as "rule-based order", rammed down their throats with the barrel of a gun or far worse.

Without NATO there wouldn't have been a war in Ukraine in the first place. Israel would think twice about bombing their Arab neighbour's kids to death without US big gun backing. The Houthi's wouldn't now be bombing merchant ships. Without the continuous US meddling presence in the Middle East millions of refugees could return home. Taking the wind out of nationalists in Europe. The brewing South China Sea conflict would remain a regional skirmish to be settled amongst themselves without a looming US shadow of WWIII. Etc, etc.

So yes, leaving NATO would be the best decision a US president could ever make since Kennedy learnt that nobody wants others stepping in their backyard (Cuba Missle Crisis). Money far better spent on updating failing US national infrastructure, internal social cohesion and quality of life (like decent health care for all US citizens)