One or two grenade-strength shrapnel devices are enough to make a $700m dollar special project useless.
https://www.marinetraffic.com/en/ais/home/centerx:72.1/cente...
You could try a surprise drone attack from a container ship. Looks like the closest ship is about 125 miles away, that might be pushing the range a bit.
They'd likely take off from the US, fly wherever they need to go for their mission without landing, and then fly all the way back to the US. Same as the B-2.
Similarly it's unlikely a drone strike is an issue due to distance.
Not a "missle base", but: "The B-52...is one of two currently at RAF Fairford in England as part of a routine Bomber Task Force (BTF) deployment." [0]
Also, more pertinent to location in scope, US has been increasing forward-based capabilities in south pacific, for example [1].
[0] https://www.twz.com/air/b-52-flies-close-to-border-of-russia...
[1] https://www.twz.com/air/massive-wwii-b-29-bomber-base-fully-...
The B-52, etc.. is just different. It's not as high value of an asset as the B-2 or the B-21 will be and gets treated differently.
https://www.pacom.mil/Media/News/News-Article-View/Article/2...
Current plans are to purchase a relatively large number of B-21's. Some losses are expected and accepted.
Ironically the B-21 is probably safest in the air. The greatest kinetic threat is on the ground because forward air bases generally lack hardened aircraft shelters or effective missile defense. This is another reason why maintaining deterrence against China will require a major increase in defense spending or realignment of priorities.
The whole point of procuring a platform like the B-21 is to never have to use it. The strategic calculus is that just having it gives the US a range of conventional options short of global thermonuclear war, and thus forces adversaries to be more cautious.