This has been an ongoing debate since the end of the major combat operations in both Afghanistan and Iraq.
I know the US Army bought some of the older CIWS systems that the USN was taking out of service and made the
C-RAM which is a system that could be mounted on HMETT that can be used against rockets and mortar shells. Which it has effectively in the last few years.
After the ballistic missile attack against the base in Iraq, there have been questions about where the US Army ADA units are. The reality is there are only so many of them and the requirements are huge if you look at it. From Iraq and Afghanistan, to Korea, Japan, Guam and on over to places like Europe where there is a need. The US Army has chosen, like it has for a number of other important missions like EW, to divest itself of that mission because of costs to buy or maintain platforms that already exist. Let alone the RDT&E for things like advance helicopters, advances firearms, uniforms, or even meals. All of which has sucked up budget line and with the every decreasing military budgets from the heyday of the 1960s. There are decisions being made based less on what could happen historically and more on what hope and pray.
For historical context the last major offensive by Opposing force air units against the US Military was the Korean War when the Korean People's Air Force was able in the opening months of the war to get in some attacks on forward operating bases where the USAF was based. That was approximately 1950. Since then the US has enjoyed control of the air during all major offensives. The only thing that has stymied them was ballistic and cruise missiles, with near misses during the Gulf War in 1991 and a direct hit, then again in 2003 when the Iraqis tried to use some HY-2 Silkworms against bases in Kuwait. Where the engagement of those Silkworms happened to be real close. Short of those threats, the only other thing has been 122mm rockets and mortar shells from very mobile platoons of men that are hard to target with counter battery fire since they have typically set up to shoot using only basic local tools and then immediately leave once the round of fire is complete. If not already left as in some weather conditions have allowed them to use things like the snow to have a mortar tube or a rocket tube already to fire allowing the melting of the snow to light the fuze or even drop the round down the tube to be fired.