The World Policy Institute speculates on Russia’s stance vis-à-vis America on Iran and nukes:

“Despite its public claims to the contrary, Moscow knows that Iran’s missile capacity poses a threat and has at times publicly admitted as much…Why then does Moscow deny the threat? The reason is simple but discomfiting to those who think Moscow will cooperate with America to neutralize Iran. Russia sees Iran not as a threat, but rather as a potential ally against America in the Middle East and Persian Gulf. It also believes that support for Iran in the form of arms sales keeps Iran from sponsoring Islamic militants in the North Caucasus and Central Asia. Moscow regards U.S. invocations of the proliferation threat as over-hyped, self-serving attempts to oust Russia from the Iranian market. And since key lobbies like Rosatom, along with the Russian energy and defense industries, make billions from profitable deals with Iran, Moscow will not yield this prize cheaply.”