Congress approves bill barring presidents from unilaterally exiting NATO - The Washington Post

A "future president might challenge such an effort and invoke the president's authorities as commander in chief under Article 2 of the Constitution," O'Hanlon said in an email. "It would, I think, be uncharted territory if this issue were forced to a confrontation." 

A Kaine aide said that while the Constitution is clear about the process to enter a treaty — including ratification by the Senate — it is silent on withdrawal. The provision offered by Kaine and Rubio was an attempt to offer specific guidance about the process, said the aide, who was not authorized to speak publicly on the legislation and spoke on the condition of anonymity...

https://www.washingtonpost.com/national-security/2023/12/16/congress-nato-exit-trump/