I might add a little bit to that, on a couple of points. Tactical nuclear weapons have been a subject of U.S.–Russia negotiations for some time. It was to be the next stage of negotiations following the strategic agreement. The Russians have never wished to go down that road. They have about 4,000 tactical nuclear weapons deployed. NATO, at last count, had somewhere below 60 gravity bombs, which is very old technology. The main impediment is Russia on the negotiation of tactical nuclear weapons. The stocks it has are way out of proportion to whatever perceived threat it may have.
The second thing is that Russia is really effectively abrogating the INF treaty by developing a very high-speed cruise missile, faster than anything the United States has. Think of that. There are some very serious arms control issues with Russia that are unresolved and seem to be unresolvable. The Putin regime basically seems comfortable with abrogating various commitments it's made.
Finally, I would endorse fully what Dick said about Pakistan. It has the most active nuclear weapons production facility in the world. It's producing more nuclear weapons than any other country in the world. It's stockpile is increasing. It's developed suitcase bombs, where the core is fused. The traditional security protocols for these weapons don't exist. Its military doctrine governing the use of these weapons is scary. If it anticipates a threat from India, the doctrine has it putting them in the backs of trucks and distributing them around the countryside. Think of that.
I could go into more detail.