So silly in fact, Putin is moving tactical warheads into Crimea.
We are not talking about ICBM mounted warheads with multiple kiloton yields. These particular warheads are sized for the battlefield.
We had similar warheads in Europe in an effort to counter the massive armored advantage the Soviet Union enjoyed back during the cold war.
Back then, the Soviets could roll columns of tanks into European nations, there was little NATO could do to stop them conventionally....then enters the above.
Use of tactical nuclear warheads would not immediately illicit a full out nuclear response continent to continent. The Russians would no doubt come under immediate worldwide condemnation, but there would not likely be a full out earth shattering exchange of nuclear arsenals as in the movies.
Russia going nuke as it attacked NATO would result in Russia disappearing and the remains being carved up into independent states and whatever China wanted.
This is a ridiculous bluff, made for the gullible.