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.
you have no understanding of how NATO works..
many NATO nations have been involved in many conflicts.. sometimes other NATO nations are involved, sometimes they are not..
without invoking Article 5, a conflict is NOT a NATO conflict and there is no requirement for any NATO nation to get involved..
As just one example France has been involved in more than a dozen conflicts since NATO was formed.. in some cases they have been part of a coalition, in some cases they have fought on their own (zero assistance from any NATO nation).. and in 1 (Afghanistan) they have participated in a NATO conflict..
Aussies and Kiwis and the South Koreans all fought in Vietnam... None of those countries are NATO.. A few NATO countries (UK, France, Canada) provided limited technical and humanitarian support but did not actually fight.. the rest of NATO sat out (it wasnt a NATO conflict)..
There were 16 member nations in NATO during Bosnia. All got involved, but Bosnia was NOT a NATO conflict, and most did not put troops on the ground (although 12 participated in denying airspace over Bosnia using their air forces)...
All NATO nations HAVE NOT participated in Anti-Piracy operations off the coast of Somalia.. There are 32 NATO member nations currently. 15 NATO nations participated in Operation Ocean Shield. 17 NATO countries sat the bench for that one.. 23 non NATO nations joined the coalition.. several of those countries are actually adversaries of the US and NATO (Russia and China, both participants in Ocean Shield, would be at the top of that list)..
Intervention in the Libya civil war was largely led by NATO countries, but was NOT a NATO action, and many NATO countries sat that one out as well.. 18 NATO countries actively participated (with the US, France, and UK doing the overwhelming majority of the heavy lifting with the other 15 countries playing much more minor roles).. 14 NATO countries played no role at all..
ALL NATO countries participated in Afghanistan because Article 5 was invoked.. ALL NATO countries voted "yes" to the conflict..
MOST NATO countries participated in Iraq.. but several did not.. because it was not a NATO conflict there was no requirement for them to do so..
Regarding "18 months ago" would NATO have stepped up and that being a "resounding yes"..
to what end?
By even the many Europeans admission on this forum Europe wasnt even prepared to adequately support Ukraine... 18 months ago, what exactly was it going to do for the US in the event of a major invasion?
Its only been since NATO started getting kicked in the balls by Trump that theyve even begun the process of modernizing and properly equipping their militaries (with a few exceptions like Poland, which has been out in front of most of the rest of Europe for a fairly long time).. Its great to say "we'll support you"... but talk is cheap.. if you dont have the tools, training, manning, or experience to do it.. then all it is, is talk..
2023 and 2024 studies show that only a tiny fraction of German armor units were operationally capable of deploying..
in 2025, by Canadas own admission, only 40% of its fighters were serviceable and available for immediate operations.. and oh, by the way, those fighters are archaic CF18's that were delivered in 1980.. the first F35 isnt going to be delivered to Canada until later this year and delivery wont be complete on their order until 2032.. those F18's are going to be 52 years old once they are all phased out of service..
and the list goes on and on and on..
Before anyone attempts "the US still flies F18s!".... The F18F Super Hornet is NOT the same animal as the CF18, which is a "legacy" aircraft roughly equivalent to the US F18 A and B models.. The F18E and F models that are still flying in the US Navy are among the most (if not the most) advanced 4th generation fighters on earth.. The US phased out the last legacy hornet in 2019 and started phasing them out many years before that.. The US has also already started phasing out the Super Hornets.. the Navy and USMC are expected to be rid of their last Super Hornet no later than 2032..