It's all so tiresome
There's a chance they won't and that's what the crazy war hawks are betting on but they could be wrong.Their whole navy is there and russia will do nothing
Iran is just as important as South Korea/Japan is for the US.
It's their main dog in the region which keeps its other assets like the Russian port in Syria in check for them.
Without it they'd be screwed.
Russia might not join in the fight but nothing is stopping them from supplying them with the latest last gen air defence systems that could make NATO rethink it's plans.