The Ukrainians are in trouble because of a general lack of artillery and SAM ammo. With decent supplies they can choke off and block any Russian attack, as they have before.
The spare ammo and SAMS the Ukrainians need, does not exist.
In the US and the West generally, we produce weapons and ammo in peacetime mode (slowly and expensively), while the Russians have been producing in wartime mode (cheap and fast).
That disparity cannot turn around in less than a decade, if we even make the attempt.