Then there's the altitude. These balloons can hang out at >90k feet. The best US interceptor, the F-22, tops out a little above 60k. Problem is, even if they got there, shooting it down is next to impossible. 6/n
The gap in altitude is sufficiently large that guns aren't an option. Neither is AIM-9X. AIM-120s are radar guided missiles. However, because the balloon has no doppler compared to the the wind and clouds around it, systems tend not to "see" it. 7/n
AIM-120 wasn't really designed to engage targets at >90k feet either. The control surfaces don't function as well at such high altitude. 8/n
MIM-104 Patriot missiles can hit things at high altitude, but again, not meant to hit things that have no relative motion to the wind.
Directed energy weapons might work, but we don't have those in service for this mission. 9/n