We have to remember that the USA isn't interested in Ukraine winning the conflict and pushing Russian invaders out of its lands. The USA is interested in drip-feeding primarily old unused equipment to Ukraine in order to degrade Russia's military capability without risking escalation. Thus the USA is cynically (and stupidly) happy to trade Ukrainian lives in order to achieve a foreign policy objective, but will do no more than this. Hence Biden's absolute rejection of sending F-16s (of any block) and when the USA says "no" so says the rest of NATO.

The reason cynical US policy is so mindless is because it totally fails to grasp the fact that Russia can win a war of attrition. Denying Ukraine essential weapons systems means that Ukraine can't counter attrition with speed and force - the only option that would lead to Russian defeat. If and when Russia finally triumphs in Ukraine, that simply means Putin's ambition will shortly thereafter embrace the Baltic nations and Moldova, which will force NATO either to act far too late in the day, or pretend that Article 5 just means sending a few medical kits and nothing more.

Either way, the spineless short-sightedness of US policy is truly depressing.