There is no basis whatsoever, except that that kind of lunacy wasn't seen during the entire duration of the Cold War, where the stakes were much higher and where the West was actively looking for an edge to take out the Soviet Union. And vice versa.
Chances are largely that he's bluffing, but there is no way to be 100% certain. What he wants to happen is 100% clear however: the West should lose its nerve and allow him to have his way.
Mind you, China would probably not take kindly either to him lobbing a bomb somewhere so would drop their so far limited support like a hot potato. No one gains if the planet gets reduced to cinders.
On the other hand, those threats also make it clear that both sides have to go back to their much more circumspect dance moves during said Cold War: NATO-on-Russia combat can't be allowed to happen.