A Test at unidentified atoll in the Pacific and resulting mushroom cloud
Let's get to the point fundamentally and unmistakably, a nuclear war would be insane.
Ever since the Cuban missile crisis in 1962, President Kennedy knew it and so did his counterpart Nikita Khrushchev in the Soviet Union. Even Stalin, probably the most brutal man ever never considered it.
That's why in the cold war between the U.S. and the USSR, MAD, mutually assured destruction were the operative words and the primary reason a nuclear conflagration never occurred because such a war was unwinnable and to contemplate winning such a war was insane.
Yes tough guy Donald Rumsfeld as secretary of defense talked of using tactical bunker busting nuclear weapons but the use of any nuclear weapons began and ended with the U.S. dropping two atomic bombs on Japan in August 1945.
Nuclear weapons today are infinitely more powerful than the bombs dropped in 1945, are Multiple Independently Targeted Reentry Vehicles-MIRV's and there are no anti-ballistic missiles capable of intercepting a MIRV nuclear weapon from hitting its multiple targets once they are unleashed. So again, any nuclear war would be insane and life on Earth could not survive a nuclear holocaust.
Dr. Paul Craig Roberts, whose writings I follow and greatly admire and has been prescient from the beginning of all the events in Ukraine before and after the coup of Viktor Yanukovych, has written, "If Putin lets Washington retain the Russian provinces of eastern Ukraine, he will have demonstrated a weakness Washington will exploit. Washington will exploit the weakness to the point that Washington forces Putin to war. The war will be nuclear." [i]
Dr. Roberts has alluded to today's world conditions as reminiscent to the time prior to W.W.I writing, "the entirety of the western media are repeating the path to war that led to World War I"  - a point this writer alluded to writing, "2014 is somewhat reminiscent of 1914 prior to the outbreak of W.W. I"only in 1914 no country possessed nuclear weapons, which is not the case one hundred years later. [ii]
And today the U.S. and Russia have the most advanced nuclear weapons in their arsenals, so MAD still applies and will prevent a nuclear conflagration.
For sure, the neo-conservatives- who were behind the coup in Ukraine that forced President Yanukovych to flee the country and bring their man Arsenly Yatsenyuk to power as the un-elected prime minister of Ukraine-may believe a nuclear first strike against Russia is winnable, apparently believing Russia would be destroyed before it could send a retaliatory strike against America and the west.
But are the neo-conservatives in Washington so detached from reality they could contemplate winning a nuclear war?
To repeat, a nuclear war would be insane.
As for Putin, thus far he has acted coolly and with restraint-contrary to the condemnation he is receiving from Obama and the west. His actions in the Ukraine crisis have been calculated and measured. Securing the Crimean peninsula where Russia's Black sea fleet is located with troops already stationed in Sevastopol was a bold move. The coup in Kiev and the instability it created forced his move in Crimea as he knew the majority were ethnic speaking Russians and would support him.
Putin supported Sunday's referendum vote by the people of Crimea to join the Russian Federation. Yesterday he formally recognized Crimea as a "sovereign and independent state".
And earlier today, in a speech before the Russian Duma, Putin declared his intention to make Crimea part of the Russian Federation saying, "Crimea has always been an integral part of Russia in the hearts and minds of people." He spoke hours after submitting legislation to begin the process of formal annexation of Crimea in Russia.