He should propose a bill to repeal 2023 National Defense Authorization Act that requires a 75% of votes in Congress to withdraw from a treaty.
It’s easier to stay in NATO but do the very minimum. Reduce the troops in Europe to only couple hundreds, send them to the Middle East. If Russia attacks the Baltic countries, provide intelligence, etc. but no troops. If troops are needed create impossible rules of engagement, as many countries did in Iraq war: not in combat zones, only go to combat in daylight, etc.
If there’s conflict like Ukraine, Libya, etc just tell them “Not American war”. Maybe tell Xavier Malei that Argentina may want to reclaim the small group of islands called Malvinas.
Finally, this is optional, ditribute books on how to speak Russian since the younger generation may not speak the language.
I am no expert I’ll leave it to others but generally - I think- the law is considered to be the Constitution and cannot be overridden