House Intelligence Committee Chairman Adam Schiff Adam Bennett SchiffSchiff to subpoena top DHS official, alleges whistleblower deposition is being stonewalled Schiff claims DHS is blocking whistleblower's access to records before testimony GOP lawmakers distance themselves from Trump comments on transfer of power MORE (D-Calif.) said late Tuesday that House investigators are looking into who President Trump Donald John TrumpBiden says voters should choose who nominates Supreme Court justice Trump, Biden will not shake hands at first debate due to COVID-19 Pelosi: Trump Supreme Court pick 'threatens' Affordable Care Act MORE's personal attorney Rudy Giuliani Rudy GiulianiThe Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting CIA found Putin 'probably directing' campaign against Biden: report Democrats fear Russia interference could spoil bid to retake Senate MORE was speaking to on a call with a mysterious "-1" phone number.

Schiff confirmed during an interview with CNN’s Anderson Cooper that House Democrats were looking into the owner of the number, which was included in call logs released by the Intelligence panel on Tuesday. The Democratic chairman declined to say who the number belongs to but suggested a potential link to Trump himself.

"We can’t confirm yet who that '-1' number belongs to, but certainly there was indications in the trial of Roger Stone Roger Jason StoneFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. The agony of justice Our Constitution is under attack by Attorney General William Barr MORE that when he was communicating with the president, it would show up in phone records as a '-1' number," Schiff said, referencing the political strategist convicted of witness tampering and making false statements to Congress in November.

“The President is really the one who has a lot to answer for,” House Intelligence Committee Chairman Rep. Adam Schiff tells @andersoncooper. https://t.co/gXFHcO5sXw pic.twitter.com/sPbHzJhnCI — Anderson Cooper 360° (@AC360) December 4, 2019

“Here you have Rudy Giuliani in communication with the Office of Management and Budget, in communication with the White House, and you also have presidential conduct in the form of tweets and other actions around the timing of different communications,” Schiff added.

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Schiff said further investigation to fill in gaps in the records was still necessary but maintained that "even in the absence of that, the evidence is overwhelming that the president was using Giuliani to coerce Ukraine into these investigations, and that’s documented in text messages [and] witness testimony."

“Rudy Giuliani had only one client in the administration, and that was Donald Trump, so who is he talking to in the course of this smear campaign against [former U.S. Ambassador to Ukraine Marie] Yovanovitch? Who is he talking to in pursuit of these political investigations in Ukraine?” Schiff said, adding that “circumstantial evidence” suggested Giuliani was also in touch with acting White House chief of staff Mick Mulvaney Mick MulvaneyOn The Money: House panel pulls Powell into partisan battles | New York considers hiking taxes on the rich | Treasury: Trump's payroll tax deferral won't hurt Social Security Blockchain trade group names Mick Mulvaney to board Mick Mulvaney to start hedge fund MORE.

The phone records released Tuesday showed extensive communications between Giuliani and the White House as well as other key figures in the impeachment inquiry.

The White House dismissed the Intelligence panel's report as the “ramblings of a basement blogger” and insisted there was no evidence of wrongdoing by the president.