Iran cannot achieve first-strike capability versus U.S. or Israel, will be stuck in defensive deterrent posture

On the other hand, it is virtually impossible for Iran to achieve a first-strike capability versus the United States. Any risks that Iran took in its basing mode and alert posture to get ready for a first strike against Israel could easily make it more vulnerable to a first strike from the United States. Spending its nuclear forces on Israel would leave Iran politically and militarily vulnerable to a huge U.S. retaliation. By striking first, it would have legitimated a U.S. nuclear attack, while simultaneously weakening its own deterrent with the weapons it had expended. The United States is the greater threat to Iran because it is much more powerful than Israel, and has actual strategic objectives in the Gulf. It is strategically reasonable for Iran to focus its deterrent energies on the United States, which it can only influence with a secure retaliatory force, capable of threatening U.S. forces and interests in the region.