Neither.
It's unlikely because (A) The threat of nuclear war is both unacceptable, and unrealistic. Putin might just be that stupid... he's already threatened the west with nuclear weapons and may even be eager to test them out. But from the west's POV it's a non-starter. We don't negotiate with terrorists, or terrorist threats. Threaten, or actually use a nuclear weapon and all of Europe, U.S. & Canada, and even countries like Japan declare war against Russia. An actual World War. Maybe Putin has lost his mind and doesn't care anymore... but the response so far to his aggression means he has to understand that if he goes too far, the rest of the world is not going to just roll over for him. And a nuclear weapon is a bridge way, way too far... At least I hope he realizes that.
(B) Trump? Are you F'ing kidding me? (This is not actually directed at you Chas but, rather, the expected response from the Biden Administration. Probably that... and a Ukrainian Go F Yourself too, just for good measure). There is no possible way they would place Trump in the same room as Putin, as Trump would sell him Alaska for $20 Billion and TWO Trump Towers.
The Biden Administration's counterproposal: "Vlad, you get Hillary Clinton. She will be our lead negotiator. Dasvidanya."