With the sole exception of the 9/11 attacks on the U.S., Article 5 remains untested. I cannot predict the future, but Trump has already said he'd ignore article 5 if a country is not paying the required amount.
>>>“NATO was busted until I came along,” Trump said at a rally in Conway, South Carolina. “I said, ‘Everybody’s gonna pay.’ They said, ‘Well, if we don’t pay, are you still going to protect us?’
I said, ‘Absolutely not.’ They couldn’t believe the answer.”
Trump said “one of the presidents of a big country” at one point asked him whether the US would still defend the country if they were invaded by Russia even if they “don’t pay.”
“No, I would not protect you,” Trump recalled telling that president.
“In fact, I would encourage them to do whatever the hell they want. You got to pay. You got to pay your bills.”<<<(emphasis added)
My "best guess" was in response to Trell's "what's next" question, which a interpreted to mean "what's next if Russian defeats Ukraine?" My best guess is probably the minority view, but the odds are certainly not zero.
>>>
Things might appear different were Russia to defeat Ukraine and have a few years to regenerate its military capabilities. Leaders of the three Baltic states see Russia as a clear military threat. German and Danish officials also have warned that Russia is planning for a possible military confrontation with NATO in the future. . . .
Why would we not think it possible, were Russia to defeat Ukraine and rebuild its military, that Putin might not miscalculate again, particularly if Ukraine fell due to lack of Western assistance? If the United States did not stick with Ukraine, which has cost the lives of no U.S. soldiers, would Putin believe that it would send its military to fight to defend eastern Estonia? Nothing would break NATO more surely than a U.S. refusal to defend one of the allies. That could look awfully tempting to Putin.<<<(emphasis added)
fsi.stanford.edu