I think Brexit has also been a significant factor in making UK way more xenophobic.
Personally, I don’t think it’s made the UK more xenophobic. A decent percentage of people supported Brexit due to xenophobia, and the success of the referendum made them more outspoken. Basically, Brexit is a symptom of xenophobia rather than the other way around.
Pretty low, even if Trump wins. The things preventing that scenario are two-fold:
Trump can’t unilaterally leave NATO. He would need the Senate to do it I think (I’m not 100% sure here).
Even without NATO, the EU (especially the Nordics & Poland) have sizable militaries and a defense agreement with the Baltics. It would be suicide for Russia to do that.
Personally, I’m more worried about the potential of Ukraine being left out to dry causing them to fall, immediately followed by Moldova falling, which would then pull Romania (and therefore the EU) into the war. This would not be a defensive war, which wouldn’t trigger article 5. Who knows how things would spiral from there.