I may be showing my ignorance here but, in spite of Putin being on the move again (remember Crimea?) NATO died in the 20th Century and has become a money drain on our few precious resources and massively dysfunctional.
Interestingly, NATO's Article 5, which is the provision requiring military assistance, has only been invoked once in history, And that wasn't in the 20th century but the 21st..
It came after 9/11, when NATO invoked Article 5 and members states sent troops to assist us in Afghanistan. In other words, the U.S. is the only NATO member to have benefited directly from that provision. Troops from a variety of NATO countries, including non-NATO troops from Ukraine, died to assist the United States.