All the more reason for the EU to step up in a big way to offset such a potential scenario. That lesson should have already been learned by the awful Trump years.
The EU and Canada share a common belief that security matters should be left to the warmongering Americans, while they enjoy all the benefits of the American security umbrella that they (and us) chafe under. There's a reason we're out of AUKUS after all.....
Really, the only countries that are actually serious here (and their proportional contributions show it) are the Scandinavians, the Baltics and Poland. But if Ukraine starts faltering and an American President who is weak on NATO looks likely, they'll have to recalculate about their own defence.
Countries, like Canada, France, Spain, Italy, etc which aren't directly threatened by Russia should be doing a lot more to help Ukraine right now. To put this in context, just to approach the same percentage of GDP committed as aid to Ukraine as the US, Canada would have to commit another $6-8B more. I honestly wish we would send them all our tanks and armoured support vehicles, 155mm artillery, all retiring APCs and reconnaissance vehicles, and immediately launch a $5B program to replace these over the next 3-5 years. That kit is way more useful in Ukrainian hands right now and we will have to replace it all in 5-10 years anyway.