What's the point of NATO if we just defend other countries who don't meet our requirements of NATO?
NATO is _already_ in a tough spot, many countries will fail the 2% spending on defense requirement (though I'm sure Russia is making them reconsider). We can't just be throwing NATO's guarantees around to countries who didn't make it into the alliance yet.
NATO is an alliance, and a defensive alliance at that. The line is literally drawn at Poland and Romania right now. We are debating if that line should include Finland and Sweden.
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There are several requirements to join NATO:
1. The country must want to be part of NATO (and neither Finland nor Sweden wanted to join until recently).
2. The entire rest of NATO must accept them.
3. A few other things, but #1 and #2 are probably the most important. If we get those two things figured out, everything else is cake.
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That being said: support to Ukraine economically and militarily (military aid) is still on the table and looks like its happening. Ukraine will fight its own war, but they can use our weapons while doing so.
That was enough for France when it helped USA during the 1700s Revolutionary war, and the USA certainly remembers France's help in those troubling times. The "Arsenal of Democracy" approach. We likely will offer that to Finland / Sweden if they get attacked by Russia before they join NATO as well.
But getting our blood directly involved in other people's wars is still a very difficult prospect. USA shouldn't overcommit, nor should NATO.