President Trump’s personal attorney Rudy Giuliani blasted former National Security Adviser John Bolton for claiming in his new book that the president tied aid to Ukraine to his request that the country announce investigations of the Bidens.

In an interview on Fox News’ “Sunday Morning Futures,” Giuliani – who Bolton claims was in the room when Trump made the request – said Bolton was “either a either a liar or a back-stabber.”

“He went around my back to the secretary of state and complained,” Giuliani said. “I don’t know what John’s up to. He’s either a liar or a backstabber.”

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The claim in Bolton’s upcoming book, which was first reported by the New York Times, led to renewed calls during Trump’s impeachment trial that he – along with acting White House Chief of Staff Mick Mulvaney and other high ranking administration officials – should be called as witnesses. The Republican-controlled Senate eventually voted against calling any witnesses in Trump’s trial and ultimately acquitted the president on the two articles brought against him.

Giuliani said he felt betrayed by Bolton for his comments and said he considered him a “friend.”

"I’m very angry at John because John says I was a hand grenade,” Giuliani said. “At no time, during the entire period this was going on did John Bolton, who I’ve known for ten years and consider a friend, did he come up to me and say Rudy I’m concerned about what you’re doing, I’m worried about what you’re doing. Never.”

Following Trump’s acquittal, Democrats said they are mulling over whether to subpoena Bolton to testify about his time in Trump’s White House.

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In early January, Bolton said in a statement he would be willing to testify before the Senate trial if subpoenaed to meet his “obligations both as a citizen and as former National Security Advisor.”

But last week, Rep. Adam Schiff, D-Calif., told MSNBC’s Rachel Maddow that after the Senate voted to not call witnesses, Democrats approached Bolton’s counsel to see if he would be willing to give a written statement "describing what he observed in terms of the president’s Ukraine misconduct."

Schiff added: “For whatever reason, he was willing to testify before the Senate but apart from that seems intent on saving it for his book. He’ll have to answer for that.”

Fox News’ Brie Stimson contributed to this report.