Sen. Al Franken (D-Minn.) used his joke-writing skills to sear Sen. Ted Cruz (R-Tex.). (Michael Reynolds/European Pressphoto Agency)

Since coming to the Senate, Al Franken has taken great pains to be seen as a serious lawmaker and not the goofy “Saturday Night Live”-writing comedian he once was.

But old habits die hard. In his new book, “Giant of the Senate,” Franken reveals that he hasn’t left his comedy-crafting days behind. In one passage, he relays a story about his fellow Minnesota Democrat, Sen. Amy Klobuchar, preparing a funny monologue to perform at the Gridiron club’s annual white-tie dinner.

The club, made up of elite Beltway media types, invites politicos from both sides of the aisle to deliver joke-filled remarks, and Klobuchar — per Franken’s telling — decided to run one of her punchlines by its target, Sen. Ted Cruz (R-Tex.). Cruz, a onetime presidential aspirant who is famously disliked by his colleagues. In fact, Franken devotes an entire chapter of his book to his distaste for the man he calls a “toxic coworker … the Dwight Schrute of the U.S. Senate.”

According to Franken, here’s how Klobuchar described the bit to Cruz (bear in mind that this was in 2013, when the infamous Carnival “poop cruise” was all over cable news): “When most people think of a difficult cruise, they think of Carnival. But we Democrats in the Senate think of Ted.” Cruz suggested she replace “difficult” with the softer “challenging” before finally allowing that she should “go ahead and tell your joke.”

Franken was irritated — both by what he called Cruz’s “patronizing” attitude toward his colleague, and by the pulled punch of a joke. So he suggested to Cruz his own rewrite: “When most people think of a cruise that’s full of s—, they think of Carnival. But we think of Ted.”

Now that’s a burn. Franken seemed satisfied with the reaction.

“And there went Ted’s smile,” Franken writes. “For once, he had no words.”

Cruz as the butt of jokes isn’t new. One of the harshest jabs at the Texas Republican came from a member of his own party — at a media dinner last year, Sen. Lindsay O. Graham (S.C.) offered up this gem, after  several Democrats had used Cruz as a comedic punching bag: “A good Republican would defend Ted Cruz,” he said, pausing for effect. “That ain’t me. If you killed Ted Cruz on the floor of the Senate, nobody would convict you.”