The question shouldn't be, "Could this escalate into a nuclear war?" but rather, "Am I willing for myself and everyone I know to die in a nuclear war for Zelenskyy?" The answer should be obvious.
Honestly, who could say no to that face? I regret that I have only one life to sacrifice for Zelenskyy!
Honestly, though, the time to really worry is if US troops and Russian troops are facing each other for real on a battlefield. The reason why the nukes could fly in such an instance is simple because both sides would have to be prepared for the other side launching them all at once. It's kind of funny to read people talk like Russia would launch a nuke at Washington, DC and then another one later, possible at NYC. No, they'd launch every nuke aimed at every major NATO city all at once. All our nukes would launch around the same time. I mean MAD doctrine hasn't changed, has it? The whole reason we never directly took on the Soviet Union was due to that.
But of course, we didn't have a charismatic man like Zelenskyy to make it worth it at that time. If only we had, maybe we'd have taken Stalin out back then. It's very sad that Zelenskyy was not the leader of the free world back then!