From the Sundance film guide:
In the summer of 1968, television news changed forever. Dead last in the ratings, ABC hired two towering public intellectuals to debate each other during the Democratic and Republican national conventions. William F. Buckley, Jr. was a leading light of the new conservative movement. A Democrat and cousin to Jackie Onassis, Gore Vidal was a leftist novelist and polemicist. Armed with deep-seated distrust and enmity, Vidal and Buckley believed each other’s political ideologies were dangerous for America. Like rounds in a heavyweight battle, they pummeled out policy and personal insult—cementing their opposing political positions. Their explosive exchanges devolved into vitriolic name-calling. It was unlike anything TV had ever broadcast, and all the more shocking because it was live and unscripted. Viewers were riveted. ABC News' ratings skyrocketed. And a new era in public discourse was born.
It's a lot of fun watching these two insult each other. They have such a command of the English language that their insults almost sound like poetry. Besides watching their debates, we get political scholars and other experts commenting on Vidal and Buckley's history, the political landscape at the time, and ABC's ratings. One commentator said if they wanted to end the Vietnam War, all they had to do was put it on ABC and it would be canceled within a few weeks. They also said there were only three networks at the time but somehow ABC was still fourth.
I enjoyed the movie for the most part, but I don't think it's for everyone. It helps if you're a political junkie. As much fun as the debates were, by the end of the movie I felt underwhelmed. But Dick Cavett is one of the interview subjects, so that makes it worth watching right there.