Sarah Palin says a Democratic Party invitation to the father of Orlando nightclub killer Omar Mateen to attend a Hillary Clinton rally is the equivalent of welcoming madman Charles Manson.

"WHAT? CHARLES MANSON WASN'T AVAILABLE, HILLARY?" Palin wrote in capital letters on her Facebook page.

The former governor of Alaska and 2008 vice presidential running mate of John McCain added, "How could security allow him to get THIS close to her?"

According to reports, the Florida arm of the Democratic National Committee invited Seddique Mateen to Monday’s Clinton rally in Kissimmee, an offer he accepted and which placed him four rows behind the candidate.

But Palin, who supports Republican presidential nominee Donald Trump, says the invitation never should have happened.

"Seriously, if this doesn't do her in, then what in the world could ever derail the liberals’ campaign? Unbelievable."

Seddique Mateen, an ardent Clinton supporter, is the father of the crazed gunman who burst into a gay nightclub in Orlando in June, shooting dead 49 revelers and wounding 53 others.

In an interview with WPTV following the rally, he said: "Hillary Clinton is good for United States versus Donald Trump, who has no solutions."

Palin's mention of Manson referred to the California madman who commandeered a small army of deranged hippies to slaughter seven people in 1969.

Manson's victims included Sharon Tate, the pregnant actress-wife of film director Roman Polanski, and hairstylist-to-the-stars Jay Sebring.