Kyiv could rapidly develop a rudimentary weapon similar to that dropped on Nagasaki in 1945 to stop Russia if the US cuts military aid, it has been suggested
Given the 96 deal was, Russia gets it nukes back in exchange for respecting Ukraine's borders.
Developing them may not be so stupid. Using them first, sure, stupid. As it is for any nation. But MAD was effective with Russia. While no nuke reprisal ability, clearly leads them not to give a shit about treaties they agrred to.