The rest of us will continue to work together with the US for as long as possible.
But the trust has now gone. The other countries no longer believe the US will necessarily be on the European side in a war with Russia. Even if it is initially, the GOP will screw it up if it wants leverage.
The Dems would be with NATO, of course. But you have a Republican party with a leadership that is sympathetic to dictatorship and that will undermine Dem support for NATO. And we have to be strong enough to deal with that.
US isolationism is back. The US equivalent of appeasement at the beginning of World War II. Hopefully you won't fight on the side of the Russians if Trump wins, but I don't entirely rule it out any more.
There will be 500m Europeans in the post-NATO defence organisation, so we should be capable of becoming a lot stronger. But also bear in mind that a strong Europe won't listen to the US so much any more. And I imagine countries like Japan, Australia and South Korea will align with us over a fickle partner like the US. Canada too.
Trump is already doing an immense amount of harm to US interests with his prevention of aid to Ukraine via congress and his pro-Putin stance. And the fact that the GOP voters support him tells us how deep the rot is.