Bolton, who was fired by Trump and turned against him, made the comments in a CNN interview on Monday.
“I think it’s very troubling [Trump] has said, ‘I can’t lose unless there’s fraud,’” Bolton said. “Of course he can lose in an honest election.”
The Republican nominee resisted pressure to acknowledge a peaceful transfer of power if he loses on November 3.
He further warned that “Let’s be clear: Trump will not leave graciously if he loses. He will not leave graciously. Whether he carries it to the extreme, I don’t think we know.”
Despite being officially nominated by the GOP, Bolton asserted that Trump is not a conservative or a Republican.