GOP Senate candidate Josh Mandel (Ohio). (Phil Long/AP)

That’s what happened last week when some of Ohio State Treasurer and GOP Senate candidate Josh Mandel’s cousins (on his wife’s side) took out a paid ad in the Cleveland Jewish News that blistered and even belittled him for his views on gay marriage and gays in the military.

Mandel married into the prominent, wealthy (think mega-builders) and sprawling Ratner family, nine of whom signed the “Dear Josh” letter.

“Four years ago you came into our family,” they began, and “how happy our family members were as they described it afterwards.

“So we were deeply saddened,” they said, during the Oct. 18 debate with incumbent Democratic Sen. Sherrod Brown, where he talked about his views on those issues.

“Your cousins, Ellen Ratner and Cholene Espinoza,” the letter noted, married in Massachusetts eight years ago, so “it hurts us that you would embrace discrimination against them. . .”

“Like you, Cholene spent many years in the armed forces. A graduate of the Air Force Academy . . . she became the second woman in history to fly the U-2 reconnaissance plane. And yet, you have argued that she, like many gay and lesbian soldiers, should be forced to live a life of secrecy and lies.”

Okay. A substantive discussion so far. But then it got tougher.

“This family is sprawling and diverse,” the cousins said, “but it has always believed strongly in the values of equality and inclusiveness. Your discriminatory stance violates these core values of our family.”

Then they twisted the knife. Mandel, though 35, looks like a college kid.

“Nevertheless, we hope that over time, as you advance in years and wisdom, you will come to embrace the values of inclusiveness and equality as well.”

Mandel’s campaign told the Cleveland Plain Dealer that none of the Ratners who signed the letter even live in Ohio.

“Josh has never met any of the ’cousins’ who signed that letter and has no idea who they are,” said a campaign spokesman. “He looks forward to having the opportunity to meet them someday.”

Not a bad idea since one of them is Bruce Ratner, an owner of the National Basketball Association’s Brooklyn Nets (formerly based in New Jersey) and builder of the new Barclay’s Center arena and massive Atlantic Yards complex. His brother and co-signee of the “open letter,” Michael Ratner, was the longtime president of the Center for Constitutional Rights. (Both the brothers are from Cleveland.)

Phew! Might want to pass on that invite to Thanksgiving dinner at the Ratners.