[nradov]

From Russia's perspective, tactical nukes aren't some kind of magic solution to reverse their battlefield losses. In land warfare, such weapons are most useful to knock out military bases and troop concentrations. But at this point the Ukrainian military is well dispersed and much of it is currently engaged in close combat with Russian forces. So a small nuke wouldn't kill many Ukrainian soldiers and there would be a high risk of fratricide. Most of those Russian military units are probably also not properly trained or equipped to fight on a nuclear battlefield; I suspect much of their CBRN gear has been stuck in storage since 1991.

Russia could force Ukraine to surrender by nuking population centers and civilian infrastructure. But that would come with such a high political and economic cost that I hope Putin will be rational enough not to go so far.