The other unusual thing Harry Thomason said about the Clinton years in a TV Critics Assocition panel on an upcoming two-part film on the former president was the first to break an unwritten ban on politicians on “The Tonight Show with Johnny Carson.”

Nowadays, it’s expected to see a politician make a late night appearance to poke fun at himself after a gaffe in public. Back then, it was just after Clinton had made an amusingly long-winded speech at a Democratic convention in his first platform before a national audience. They had to do something, his backers thought, so Thomason and his wife Linda Bloodworth Thomason devised the Carson appearance.

Except that Carson didn’t have politicians on the show. So Thomason says he called producer Freddie de Cordova to plead his case.

“And I said, ‘Freddie’ and he said, “It’s not any use. I’m not going to be able to change this.” I said, “No, listen to me. He’s going to come on the show as a musician. He’s going to play the saxophone.’ ”

“And so he starts laughing, and he said, ‘It’s not going to work, but I’m going to go talk to Johnny.’ And he called me back in 15 minutes, and he was laughing. He said, ‘Carson said for him to get that saxophone and get out here Tuesday night.’

Thomason said he called Clinton and told him to start practicing. The appearance went well, with Carson doing a gag, pulling out an hourglass to remind the ambitious politician not to go on and on.

And, Thomason says, “that’s how politicians started appearing on late night shows.”

More history lessons are planned in the “American Experience” production, “Clinton” Feb. 20 and 21 on PBS.