The US should offer to withdraw from NATO and make Ukraine our 51st state. This is a potential win-win-win solution for Ukraine, Russia and the US.
Russia wins because Ukraine is no longer a member of NATO. Keeping nuclear weapons out of this territory could be an additional bilateral agreement between Russia and the US. The desirable Crimean peninsula could be partitioned between Russia and the US so we both get access to a prime shipping port.
The US wins because we get a footprint in Europe for shipping and vacationing. And oh yeah, we avoid world war 3. Not to mention we have a moral obligation to take care of Ukraine after they gave up their nuclear weapons at our insistence. Why would Iran and North Korea do the same if we are proven unreliable liars. Additionally we get access to Ukrainian minerals and Russian oil. And if that weren't enough, this would strengthen our European alliances as a counterbalance to a growing China.
Ukraine wins because they get security and the democracy they voted for, albeit as a US state. Future independence could be optionally negotiated. Ukraine would have to choose this via a fair election to be valid. If we make clear they are on their own if they reject the deal, I suspect this path would be attractive.
Oh, and if it isn't too much trouble can we make English an official language there. That would really cement the deal as an attractive vacation spot for me to visit.
Colonization has become a dirty word. Does it have to be ? Australia and the US were colonies and they turned out OK. If Ukraine chooses colonization it seems a win-win-win to me.