So I watched.
Here's where my ears pricked up:
"By 1973 I was in a state of kind of shell shock and sitting on the sidelines..."
Now, there's another gewgaw for the desk drawer ....
In 1973, the man was deep into his Black Panther period, which ended with the murder of Betty van Patter, whose body would be found in January 1975, causing Horowitz finally to notice, so he claims, that the Panthers were violent actors. This is not exactly "sitting on the sidelines."
Still ahead of him also in 1973 was his June 1974 essay in Ramparts pushing back against Solzhenitysn. Yes, at age 35, in the era of Comrade Brezhnev, David Horowitz was still extolling the "Soviet experiment" for "its gains in the material realm, and in science, public education and health"; as a "still-powerful beacon" to the Third World; and fully expecting it to "fulfill the promise of October" over the evidence of The Gulag Archipelago.
See for yourself: