Russia supports Iran, not because they have any great love for Iran or Shiite fanatics, but because Russia is a rival of the United States and anything that weakens the United States strengthens Russia.
Russia’s greatest hope, probably, is that there’s a military confrontation which results in a lot of Persian Gulf oil facilities being destroyed, and that those Sunburn anti-ship missiles that Russia sold to Iran sinks a whole bunch of American ships. As a petroleum exporting nation, Russia wants the price of oil to go as high as possible, and they would also enjoy seeing the United States suffer a military defeat at the hands of Russian military technology, because that would weaken the United States and give Russia a profitable business in selling their missiles to anyone who wants to buy them.
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I should also point out that it’s a really bad idea for the United States to keep expensive warships in the Persian Gulf where they are sitting ducks. They ought to be parked in the Indian ocean, out of range of Iranian missiles, from which point we can relatively safely bomb them back into the stone age.