> Ukraine didn't have nuclear weapons. America does
So? If nuclear war is always an intolerable choice for America, then America's nuclear weapons will never be used in any case, and any aggressor who can plausibly threaten nuclear war is free to seize anything from America with that threat.
If nuclear war isn't always intolerable, then, well, we've eliminated the premise off the upthread argument about Ukraine, and are in a different discussion.
The intolerability of nuclear weapon usage is not a simple binary. We didn't have the same kind of security agreements with Ukraine that we do with NATO countries, hence we are not at war with Russia.
Had Russia invaded a NATO country, we still would not have launched first, but rather used conventional weapons, given the fallout (literal and metaphorical), but actually using them to prevent greater numbers of casualties from protracted war is not fully off the table, so to speak.
So? If nuclear war is always an intolerable choice for America, then America's nuclear weapons will never be used in any case, and any aggressor who can plausibly threaten nuclear war is free to seize anything from America with that threat.
If nuclear war isn't always intolerable, then, well, we've eliminated the premise off the upthread argument about Ukraine, and are in a different discussion.