It might be a good idea for Herman Cain to stop digging. After trying to fend off accusations of sexual harassment, he upped the ante in the last debate by referring to Rep. Nancy Pelosi (D-Calif.), the first female speaker of the House, as “Princess Nancy.” Not content with lighting up the figurative “does not respect women” neon sign over his head, he next decided to joke about Anita Hill. Politico reports:

Herman Cain told New York journalist Fred Dicker Friday that a joke he made about Anita Hill was “in no way intended to be an insult to Anita Hill or anybody else.”

Cain was caught on camera Thursday joking about the possibility of Hill — who accused Clarence Thomas of sexual harassment during his confirmation hearings — endorsing him for president. The Republican presidential candidate recounted the moment on Dicker’s radio show. . . .

Cain said he expected that all his public comments would be picked apart at this stage of the presidential race, grousing that he’d seen an article this morning that signaled the reporter had reached out to Hill for comment.

“Why do you need to go contact Anita Hill?” Cain asked.

Cain seems determined to convert his nice-guy persona into “quintessential jerk.” If his goal is to come through this with his dignity and personal reputation intact, he’s doing himself a real disservice.

Cain appears to be someone who simply doesn’t understand how he comes across to others, especially to women. When everyone is laughing at his jokes, he’s sunny. But under scrutiny, he digs his heels in, becomes downright nasty and runs the danger of losing the benefit of the doubt that so many have been extending to him.

It is all taking a toll on his ratings and favorability. According to the InsiderAdvantage poll, Cain’s support has fallen among caucusgoers in the course of five days from 30 percent to 23 percent. In the CBS-New York Times national poll, he’s gone from 25 percent in late October to 18 percent. (A note of caution on this poll: It is an outlier among surveys, showing both Cain and Mitt Romney below 20 percent. Perhaps the small sample of GOP voters is responsible.) Likewise in the McClatchy-Marist poll, Cain has sunk below 20 percent.

It’s not all that surprising that he is losing altitude steadily. He’s losing ground with Tea Partyers (down in the CBS-New York Times poll to 19 percent from a high of 32 percent) and women. Not only the sexual harassment allegations but his faulty command of basic knowledge is beginning to sink in among GOP voters.

It might not be all that surprising that his poll numbers haven’t fallen off a cliff; His supporters and even those conservatives who don’t like him all that much feel duty-bound to stick by him as a protest against the mainstream media when pollsters come around. His last two debate performances have been mediocre at best, and if he continues to falter (very likely in foreign policy debates) voters may no longer feel obligated to defend him. Moreover, when it comes to actually voting for him, voters very well could drift off to other not-Romney candidates.

The bottom line is Cain has surely reached his peak and now is beginning his downhill slide. The only question is whether he passes Rick Perry on the way down.