Ukraine has been in war economy mode for over a year now, and it's not sustainable long term while all of the sanctions on Russia haven't crippled their economy to the point of being unable to continue fighting. Their ability to fight Russia is largely dependent on continued western aid, largely from the US, which has become increasingly controversial politically. The current counteroffensive has been a slow, long grind without much in the way of territorial gain so far, further decreasing popular support for Ukraine in the west. If Russian sympathizers in the US government manage to block aid to Ukraine before they are able to break Russia's defenses, the Ukrainian Armed Forces will run out of funding and equipment and be forced to negotiate best case scenario, or be overrun by the Russians worst case scenario. It is still a long time until the next US election so they should still fight, but unless they're able to make dramatic gains like they did previously, Ukraine may have to negotiate eventually