But the US military is not engaged in a war with Russia in Ukraine. Congress would need to declare war for that to be the case. So why should we so easily accept the premise that the US military is responsible for purchasing equipment and delivering it to war zones in countries where we have no troops, to be used for killing soldiers with whom we are not at war?

It’s military aid, not arms sales. There’s little incentive the resources be used efficiently. That way there can be more aid bills. It’s what people voted for I guess.

Instead, Congress has declared military aid to Ukraine. The US military is responsible for doing whatever they are told to do by our civilian leaders.