Most European politicians are quite clear that Ukraine cannot be forced into giving up territory, must be able to defend itself and must be free to make decisions about it's own future with regard to membership of NATO, Trump knows this so my guess is that he's trying to find a way of stopping US support for Ukraine rather than expecting to get peace.
Europe is already paying for more of the weapons produced by the US so it's in everyone's interests to deal with Trump diplomatically rather try to bully the bully. Ukraine needs things only the US currently can provide, European countries need to prevent Putin gaining strategically important parts of Ukraine and Trump is a totally loose cannon. No wonder politicians are being restrained.