It would be a clear violation to display political/campaign items when in uniform/on the job (for any govt. employee.)
Does the usaf really believe that maga hats are "personal items" and not campaign materials?
"There is no rule against Airmen bringing personal items to be signed by the president," USAFE said in a statement.
There they are for sale (on the campaign web site):
https://shop.donaldjtrump.com/?utm_source=website&utm_medium=web&utm_content=top_nav
I'd say the usafe is full of sh it.