[jfengel]

That's exactly it. Up until now, it was widely believed that this would risk nuclear war, which is why it wasn't allowed.

But now the US is about to have a President who is far, far more favorable to Putin. Would Putin blow up the US just before it's going to cease support for Ukraine entirely?

This is a calculated risk. Everything about this war has been a calculated risk (and indeed, any war). There is a strong argument to be made that nuclear war was never really going to happen, and that we should have allowed Ukraine to attack Russia more directly all along. The present administration rejected that, but now that calculation has changed.

Is it correct? Who the heck knows.