Something to consider:
A big victory in Ukraine this fall would be good for the democrats, one during the J6 hearings, not so much, as it would steal the news. So for a few weeks, while the J6 panel was holding their public hearings, a stalemate would be best for the democrats. Could this be a factor in throttling the Ukrainians? The Russians are still attacking and being destroyed doing it, so the imperative might not be so great, as they need to be worn down more. Territory can be regained later, the point is to keep destroying irreplaceable equipment and troops too.
It would be bad timing for Ukraine to be rolling up a shattered and collapsing Russian army in spectacular gains making headlines, while the J6 panel was holding public hearings from key witnesses. Joe would not want this, the Ukrainians and key allies would not want this either, they know the republicans are a bunch or traitors under the control of Trump and bad news for them. So something to consider, but it would have to be carefully done and the cards held close to the chest. There may be more at play here than being afraid of Vlad, I really don't think Joe is afraid of him, just playing smart, both at home and abroad. He is having a run of bad luck lately though, largely through no fault of his own, he admits his mistakes though and that means he can learn from them. It's something Trump could never do, admit his mistakes or learn anything at all, or even evolve as a human being in any way past childhood.