Ivanka Trump is also a senior presidential adviser. "Jared is a fine man, you know that," the former New York mayor said. "Men are disposable." "But a fine woman like Ivanka? Come on." Tweet "'Ivanka Trump? I think I would get on my charger and go right into ... their offices with a lance if they go after Ivanka," the former federal prosecutor said of Mueller's team. Giuliani also predicted that "the whole country will turn on," Mueller if the special counsel went after the president's daughter. Mueller is investigating Russian interference in the 2016 presidential election, as well as possible collusion by Trump campaign officials.

Rudy Giuliani, former mayor of New York Anthony Behar | Bloomberg | Getty Images

In June 2016, Trump's son Donald Jr., Kushner and then-campaign chief Paul Manafort met with a Russian lawyer, Natalia Veselnitskaya, at Trump Tower in New York. Donald Trump Jr. accepted the meeting with Veselnitskaya after he was told she had incriminating information about former Secretary of State Hillary Clinton, who was running for president against his father. Veselnitskaya told NBC News this year that after she left that meeting and was waiting for an elevator, she exchanged pleasantries with a woman she believed was Ivanka Trump. A source familiar with the meeting told NBC News that it was in fact Ivanka Trump. The Los Angeles Times reported in January that Mueller's investigators are interested in the Russian lawyer's encounter with Ivanka.