[tzs]

What about North Korea? They might be crazy enough to do something like that, especially if they are pretty sure it could not be tracked back to them.

Actually, looking at current high altitude wind patterns [1] it looks like launching a high altitude balloon anywhere in a large chunk of the Northern Hemisphere will get it to the Northern US, including most of the Mideast, which includes many of the places with people that would love to do a terrorist attack on the US. If one of those places did it, though, their balloon would have to pass over Russia and/or China so probably wouldn't go undetected like a North Korea launch might. Russia and/or China might not be happy to be used that way.

[1] https://earth.nullschool.net/#current/wind/isobaric/70hPa/or...