I think some in this thread are missing an important point. A nation does not need to be able completely defeat another nation on paper to obtain deterrence. Let's use Iran's air defences as an example. Iran integrated air defence (IAD) does not need to be able to destroy the whole USAF, it needs to be enough to potentially cause enough casualty to make the US not think about such a conflict. Iran's IAD is capable today to cause such damage to US air damage and it is growing at an impressive rate. Keep in mind, In above scenario I only focused on air defence, obviously there will be many other factors to consider in an actual conflict, such as Iran's vast missile forces.
First of all, you do realise Iran has dozens and dozens of vast underground missile bases that are 100's of meters below ground and in some causes mountains? US has no hope in hell to destroy these. This is not Hollywood. Furthermore, another chunk of Iran's missile are highly mobile and are always on the move (to avoid satellite intelligence).
Furthermore, Iran is keeping an eye on everything in this region. If US coughs, Iran will know it. US has no chance of a surprise attack on Iran. Not in a conventional military sense anyway.