The Europeans are irrelevant and i think Trump will just ignore their yapping. He despises most of them anyway. But Ukraine can definitely reject. The question is what will the US do in response?

Will Trump go through with the threat to cut off all military and intelligence support? Without US intelligence and US battlefield communications systems the entire Ukrainian army probably collapses within weeks. Europe can keep pumping cash and a trickle of weapons, but it just doesn’t have the capability to replace the US’s ISR.

Or he could apply more pressure with the anti-corruption investigations angle, though i think that the “anti-corruption” apparatus in Ukraine is more a European tool than it is a US one. Trump could very well flip flop again, or he could chicken out, not wanting the bad PR of being blamed for a Ukrainian collapse. I think Kiev and its European allies can try to blackmail Trump with this angle, but if Trump has the balls he can just call their bluff.

Of course this is assuming that Trump actually wants to end the war, which is not necessarily the case. He probably mostly just wants to pawn it off on the Europeans but in a way that doesn’t make him look weak.