Russia and Iran aren't really that friendly, they're mere allies of convenience, I doubt Russia would intervene directly there. Maybe covertly send some arms, but nothing that could really stop the US from bombing Iran; iirc the Russians have been unwilling to sell their latest anti-air system to Iran.
I agree that the Iran threat is overblown, even if they really tried to acquire nuclear weapons, they could probably be deterred...but as far as is known, they actually ended their nuclear weapons programme in the early 2000s. The whole "They're building nuclear weapons!" argument is totally fake.
Problem is with the current US leadership imo, Trump is a very weak person with no real principles of his own, and he's got crazy advisors like John Bolton (those old enough to remember the 2003 Iraq war will know what that means...).
With Iraq it was WMDs, with Iran it's WMD possibilities, and with Venezuela it's "the people aren't being treated fairly"......there's always some sham justification for wars and potential targets ot get the masses to fall in line.