I still don't see how the force the US has deployed in the region is sufficient to significantly damage Iran. Unless the US and Israel can knock out most Iranian missile launchers in the opening strike, Iran's potential counter strike could be devastating. I am not sure if they have enough Patriot batteries moved into the region to meaningfully disrupt Iranian missiles.
I suspect if the US strikes Iran it will be because they have convinced themselves that they have the ability to destroy Iranian missile launch capabilities to such an extent that their defensive systems will be able to deal with whatever Iran can launch in retaliation. If the US doesn't end up striking Iran it will be because they don't believe they can meaningfully destroy enough of Iran's launch capability and the resulting counter strike would overwhelm their defense with devastating consequences.