House Intelligence Committee Chairman Adam Schiff is planning to subpoena President Trump's personal lawyer Rudy Giuliani "as soon as first thing next week."

"We're gonna need evidence from Rudy Giuliani," Schiff said during an appearance on Sunday's 60 Minutes. "And it's our intention as soon as first thing next week to subpoena him for documents. And there may very well come a time where we wanna hear from him directly."

Giuliani has asked the government of Ukraine to investigate former Vice President Joe Biden and his son Hunter Biden's ties to an energy company owned by a Ukrainian oligarch, a request Trump repeated during a July phone call with the country's leader.

While he was still vice president, Biden, who is currently the front-runner in the Democratic primary and likely to take on the president in 2020, threatened to withhold $1 billion in U.S. loan guarantees if the country did not fire it's top prosecutor, who was investigating the company that employed his son as a board member.

Trump's call was part of an intelligence community whistleblower complaint released last week, and House Democrats announced an impeachment inquiry into the president on Tuesday.

Schiff's indication came hours after he told ABC's This Week that the whistleblower behind the complaint has agreed to testify before the House Intelligence Committee, of which he is chairman, "very soon."

Trump demanded on Sunday to meet with the whistleblower, who did not have direct knowledge of the phone call with Ukraine, and for the identity of the person who passed the details of the conversation along. The whistleblower, however, "fears being put in harm's way" by Trump and his allies, who are offering a $50,000 bounty for information on the person.