"We had a Muslim president for 7 1/2 years," Sabato said. "I don't believe he is [a Christian]."
Trump, who spearheaded the birther movement, repeatedly questioned whether the president is an American and if he is a Muslim.
Obama has repeatedly said that he is a Christian.
Sabato said that for the last 7 1/2 years, he has "seen this country take a bad turn" under Obama's leadership.
"This guy made it really hard for me to support him," he said about Obama, saying that the president entered office with an agenda to move the country to the left.
He said that police officers and the military don't like Obama and implied that he was not American.
"I believe that he's on the other side ... the Middle East," Sabato told ABC News. "He's with the bad guys."
He said that he was not concerned about vocally supporting Trump in liberal-leaning Hollywood and didn't care if that caused people to judge him.
"So be it," he said.