CHER’s family is being ripped apart by another nasty family feud, this one sparked by politics!

The singing legend threw all her diva might behind President Obama while coldly turning her back on her son Chaz’s beloved stepmother Mary Bono Mack. The widow of Cher’s ex-husband Sonny Bono, Mary lost her hotly contested re-election bid in Palm Springs, Calif.

The ugly snub “has once again alienated” Cher’s transgender son, who was a huge supporter of his Republican gay activist stepmom, a close family friend revealed.

“Cher set off a mas­sive blowup by completely ignoring Mary,” the source added. “What it boils down to is she was too busy tweeting her support for Obama that she couldn’t be bothered to think about Mary’s campaign.

“Now, Mary resents Cher’s betrayal, and both she and Chaz blame Cher, at least partly, for los­ing the election.”

As The ENQUIRER recently reported, ultra-liberal Cher, 66, trashed GOP presidential hopeful Mitt Romney in a series of posts on her Twitter account. At the same time, Mary was mired in a tough campaign to keep her seat in the U.S. House of Representa­tives, which was held by Sonny before his death in a 1998 skiing accident.

According to the source, Cher has long been a thorn in Mary’s side. “Mary has always gone out of her way to avoid confronta­tion with Cher,” said the insider. “Even when Cher stole the show at Sonny’s funeral with her over-the-top eulogy, Mary bit her tongue.

“In this case, though, Mary assumed that with Chaz’s passion­ate backing, she could depend on Cher. But no such luck.

“It’s as if Cher can’t re­sist stealing the spotlight from the woman who gave Sonny the happiest days of his life.”

On the other hand, Chaz ap­preciates how Mary and the Bono clan stood behind him during his gender reassignment transition, giving him even more support than Cher, says the source.

“Cher’s diva antics have once again caused bad blood in her family,” revealed the insider. “It just goes to show that she is so self-absorbed that everything must focus back on her – even if it cost Mary her job.”