LONDON (Reuters) – President Vladimir Putin, who rules the world’s biggest nuclear power, has repeatedly cautioned the West that any attack on Russia could provoke a nuclear response. Will Putin use nuclear weapons, how many such weapons does he command and how might the United States and the U.S.-led NATO military alliance respond? WILL PUTIN GO NUCLEAR? Much depends on how Putin perceives the threat to the Russian state and his rule. Putin casts the war in Ukraine as an existential battle between Russia and the West, which he says wants to destroy Russia and grab control its vast natural res…