Biden's calculus was that the American people wanted out. If that was the criteria, America would never engage in any war overseas. Did Americans want to invade Afghanistan in the first place? Osama Bin Laden wasn't Afghani and nor was he killed in Afghanistan. Did Americans want to invade Iraq? GW Bush Cheney and Rumsfeld did because "he tried to kill my daddy" and told lies to justify it.
How many Americans died in Ukraine last year? Do most Americans want Russia defeated? (The answer is yes). Is it better that Ukrainians fight Russia now or that Europe fight them later, assuming Trump wins?