"All I can do is speak the truth," Giuliani told Fox Business' Maria Bartiromo. "I've been threatened. I lost clients. I lost friends. I've been investigated by the southern district of New York for no reason at all except harassment. They've done everything to silence me they can possibly do. All that does is make me more determined because they are hurting my country very, very badly."

Last week, the New York Post published several stories based on material Giuliani provided the newspaper.

"What they leave behind in Ukraine and China, in Russia, is the impression that we're a corrupt country, that all of us are corrupt," Giuliani told Bartiromo.