The Iranians can significantly crimp the US supply lines coming out of Kuwait City and up the Tigris and Euphrates River valleys to the major supply bases in the Baghdad region. Pat Lang at Sic Temper Tyrannis maps the major US logistical system in Iraq. Note that there is a massive, brittle single point of failure system as the entire supply line relies on one major and a couple of minor highways from Kuwait to Baghdad. These lines can be cut off by motivated light infantry shooting at trucks and laying mines/IEDs.
The second, and more practical point is that the US does not have enough strike assets in the region to mount a campaign similar in size and intensity to the one used to start the invasion of Iraq in 2003. That operation is the minimal probable operation as Iran has not been under siege and limited aerial attack for the past fifteen years while Iraq had been under siege for twelve years. And the US is not able to move any significant naval strike assets forward.
The Yorkshire Ranter is performing an invaluable service in tracking down where the US carriers are and what their availability for combat looks like:
Carl Vinson, Theodore Roosevelt, Abraham Lincoln, George Washington are all in deep refit. Enterprise and Harry S. Truman are still at the stage of doing CARQUALs, in the Big E's case for reserve squadrons, Ronald Reagan arrived back in San Diego on the 20th April, and Dwight D. Eisenhower was due in Norfolk on the 23rd of May.
John Stennis and Nimitz are currently on station in the Gulf of Oman, the latter ship having just steamed back from Somali waters. Kitty Hawk is due out of Yokosuka for her summer cruise soon, but is tied to the North Pacific by her commitments there. Stennis sailed on the 16th of January, so is due to turn for home on the 16th of June, Nimitz being on station until September.
However much cruft is retailed to the press, literally no reserve exists in the fleet. (It's also worth remembering that the Charles de Gaulle returns toFrance soon.)
Despite the bluster and the ratcheting up of empty threats, the US will not be going to war against Iran anytime soon (hopefully never).