Trump is fine with Ukraine attacking Russia, that is why they provoked the war in the first place. The problem is the consequences of the war on Iran, which is now becoming unmanageable for the US and is risking global economic crisis. Russia has the means to alleviate some of this, and the US has interest in maintaining the war while lowering sanctions. Ukraine is caught in the middle, as is the fate of all vassals when the wind blows the other direction.