Fine.
I guess I'll explicitly answer your question.
The US motherland gets invaded. Or more realistically, you guys need to fight China for Taiwan, or S Korean... again. Would NATO step up?
18 months ago, that was a resounding, 100% yes. No doubt. No hesitation. There's historical precedent; Bosnia. Kosovo. Afghanistan. Libya. Iraq. Afghanistan. Anti piracy support in Somalia. Anti drug support in S America. Australians and new zealanders died in Vietnam, and brits and aussies died in Korea.
The nato nations trusted that the US would honor its nato commitments, and in turn they'd follow theirs. It's a trust based system, and the trust was never in doubt.
Today, the situation is a little different. Most nato members don't 100% trust that the US would do the same. Unless it benefits them.
There's a very high probability that this administration would demand bribes or other forms of payment in order to fulfill their obligations. Just the same as they did for Ukraine, and are trying to do with Greenland. Many seriously worry if they'd fulfill then at all. The more nervous (and frankly, slightly silly) ones see a world in which the us might even be the enemy. The trust is gone, or at least is seriously degraded.
In that context, well. It's hardly unreasonable for other nato members to play the same game. Oh no, the us is being threatened and you want nato support? Let's chat about those tariffs, maybe a bit of reverse lend lease is in order... etc, etc.
The US wants a purely transactional foreign policy. Only fair to give them one.
For what it's worth, I don't think relations have broken down to the point that the support is really in any doubt. NATO would still step up, the alliance would survive.
But even the fact that it's a question... is a big problem.