If the west crank up things already happening - stopping Russia's oil trade and blowing it it's refineries etc - it would probably get so weak economically that it couldn't really continue the war. At that point you could make a deal, or maybe the Russian government would change or decide it has better things to do.
The trouble with just signing a piece of paper is Putin tends to just ignore those.
I suppose that could work assuming the russkies don't respond to a direct attack on their refineries by escalating to nuclear war, but even so nobody's even trying that. Ukraine is too busy fighting for survival with what scarce resources they have, and none of their backers are even talking about joining the war as true allies.
My point is, it seems like everybody at some subconscious level sees this as Ukraine's problem alone, because even their most ardent supporters aren't treating Putin ss the grave international threat they call him rhetorically. Trump's being pragmatic by trying to end the war on terms that can at least preserve what's left of Ukraine as an independent nation.
The trouble with just signing a piece of paper is Putin tends to just ignore those.