On January 7, US president Donald Trump promised to withdraw the US from 35 international organizations and 31 UN agencies:
The Memorandum orders all Executive Departments and Agencies to cease participating in and funding 35 non-United Nations (UN) organizations and 31 UN entities that operate contrary to U.S. national interests, security, economic prosperity, or sovereignty.
Unverified: then the White House deleted the announcement from their website (personal note: I did receive 404 on it for a while).
Correction: announcement is still up or has reappeared. An archived copy is also available in case they change their mind.
Yes it would come back but it would be a good long while because we are having to start from the bottom all over again.
That’s the part you seem to not be getting. We are talking a process that would take YEARS to get done, if it would even happen at all.
How much of NATO is actually needed in the short term? The last bit there was kind of going in that direction. Just being a nuclear power that would credibly respond to actions against any member seems like it would provide safety for a few years.
Over the longer term, a coordinated structure to respond to novel threats starts to matter.
Given Russia is looking to take Ukraine and likely the other former Soviet countries and now we have the US is eyeing for the western hemisphere you are going to need NATO as a whole.
As for nuclear deterrence that only works if you are willing to use it. And I doubt France or the UK is willing.