[water8]

The idea is that Poland is less of a threat to Russia than the US and less likely to trigger a large escalation that potentially confronting the US would mean. It's basically the equivalent of a pawn supporting a knight vs the queen supporting a knight

[powerapple]

Maybe the idea is that Poland is reachable by Russia, making it easier for skirmishes, to escalate the situation for Russia. Then US can say: look, I knew Russia wouldn't stop at Ukraine.