I was thinking that “open skies” ended when Francis Gary Powers was shot down, I could be wrong.
Sometimes wisdom is just being old and remembering stuff that young folks don’t even know about.
“https://www.cnn.com/2017/08/09/us/russian-air-force-tu154-overflight-dc/index.html“
No ... totally different. Wiki-hahahaha-pedia has a relatively decent page on the Open Skies treaty.
The U2 flights over the USSR were basically because we could get away with it. Until we couldn’t. Then we developed (and continue to develop) other means. Oddly enough, the U2 still flies, but not over seriously denied or contested territory.