It's the low morale and poor training quality of its soldiers. Ultimately, Russia lacks leverage, because it is losing ground and losing people on the battlefield. That is the thing that we have to make sure continues. We cannot let them have a ceasefire when they could put their mobilized troops through deliberate training and therefore improve their capabilities. We also cannot let them start to grind away at the Ukrainians in traditional fighting, because the Ukrainians lack the firepower to hold them back.
That is the critical point of leverage we have that will always keep the Russians on their back foot.