"If you recall five months ago, I introduced Donald Trump," Arpaio said, introducing Trump as the rally in Mesa, Arizona. "At that time, I said a few things, we have something in common—the birth certificate investigation, which is still going on."

Both Arpaio and Trump have been vocal members of the "birther" movement which claims Obama was born in Kenya. At one point, Arpaio set people to Hawaii to investigate whether Obama was really born in the U.S.

MSNBC's Chris Matthews had asked Trump after Tuesday night's Republican presidential debate whether he was "honest when he says that Barack Obama isn’t a legitimate president."

Trump dodged the question.

"I don't talk about that anymore," he eventually replied.

Watch Arpaio's introduction:

This post has been updated.