WASHINGTON-— President Donald Trump’s personal lawyer, Rudy Guiliani, who has been at the center of the controversy that has led to calls of impeachment, confirmed Tuesday that he has hired assistant Watergate prosecutor Jon Sale to represent him in in the congressional impeachment inquiry.

Last week, Democrats opened an impeachment inquiry to look into allegations that Trump leveraged military aid to Ukraine to pressure that country to investigate former Vice President Joe Biden and his son for business ties to the country.

Giuliani has publicly acknowledged his efforts to press Ukrainian government officials to open an investigation into Biden, and has said he contacted Ukrainian officials at the direction of the State Department and that he has briefed U.S. diplomats on his conversations.

On Monday, Guiliani was subpoenaed by House Democrats for documents related to his dealings with Ukrainian officials.

In a letter to Giuliani, three House committee chairmen said a "growing public record" indicates that Trump, Giuliani and others appear to have "pressed the Ukrainian government to pursue two politically-motivated investigations.”

Giuliani responded to the subpoena on Twitter Monday, saying “It raises significant issues concerning legitimacy and constitutional and legal issues including ... attorney client and other privileges. It will be given appropriate consideration."

Giuliani appeared on Fox News Monday night, hours after he was subpoenaed for documents, saying he "doesn't know" whether he would testify. “I’m weighing the alternatives. I’ll get all my evidence together, I’ll get my charts.”

“I don’t know, if they let me use videotapes and tape recordings that I have, if they let me get some of the evidence that I gathered,” he continued.

Contributing: Michael Collins, David Jackson, William Cummings, Deirdre Shesgreen, Jeanine Santucci