America's military was designed to work either as an integrated whole, or as a surgical strike system.

In full scale war, the expensive, ultra precise weapons hit weak spots, the troops on the ground then immediately exploit the response collapsing to take ground and defeat the enemy. Meanwhile, the air defence assumes the enemy's ability to project force back will be crippled quickly.

In surgical mode, the weapons are used to take out very specific targets. Think nuclear bunkers, or taking out leadership etc. It's small scale and over before the enemy knows America is about to hit them.

In Iran, trump has tried to get the best of both worlds. He tried to defeat a large scale force using specialist weapons. However, without ground support, it needs to be used on all targets, not just high value ones. This has massively depleted America's stockpile, which took years to build.

Compounding this is that Iran has been using low value weapons to strike back. America has been forced to use defenses intended to engage high value bombers to shoot down low value drones. This has depleted their stocks of interceptors too. This has let Iran strike at the bases America needs for a ground assault option.

In short, America blew its load too hard and too fast. Iran had expected this and so didn't crumble. Now trump (and the US military) is left holding a limp dick, with no stamina left, wondering what the fuck to do about it.