Rep. Adam Schiff intends to hold President Donald Trump accountable and conduct a thorough investigation in the wake of a whistleblower complaint that led to an impeachment inquiry, the chair of the House Intelligence said on "This Week" Sunday.
"The president used that opportunity to try to coerce that leader to manufacture dirt on his opponent and interfere in our election," Schiff told ABC News Chief Anchor George Stephanopoulos, referring to Ukraine's president, Volodymyr Zelenskiy. "I can't imagine a series of facts more damning than that."
He said it's "nonsense" to suggest that explicit quid pro quo is necessary for an impeachment inquiry.
(MORE: Rudy Giuliani fires back at former White House aide who accused him of spreading ‘completely false’ theory)“It is illegal, improper, a violation of oath, a violation of his duty to defend our elections and our Constitution for the president to merely ask for foreign interference in our election,” he added.
Schiff responded to an earlier interview with Rudy Giuliani on "This Week,” saying that he was “concerned” that Giuliani or members of the Trump administration would attempt to invoke attorney/client or executive privilege.
But, he added, doing so would “be strengthening the case for an article of impeachment based on obstruction of the lawful functions of Congress.”
Schiff, Rep. Eliot Engel, chairman of the House Foreign Affairs Committee, and Rep. Elijah Cummings, chairman of the House Oversight Committee, announced the first round of subpoenas in the impeachment inquiry into President Donald Trump following a whistleblower complaint over his phone call with Zelenskiy.
(MORE: 'A bad day and a bad week for this president': Former Trump official)The subpoenas, issued to Secretary of State Mike Pompeo and five other state department officials, require documents around the July phone call and their work with the president's personal lawyer, Rudy Giuliani, to be turned over to investigators.
On “This Week,” Schiff said that the inquiry was “moving forward with all speed."
When Stephanopoulos asked why House Democrats were doing so without a formal vote in the House, he said, “It’s certainly not necessary as a matter of constitutional law that we have a vote.”
Schiff repeatedly called the whistleblower -- who has not been identified -- courageous for coming forward. He said the complaints had been “substantially corroborated,” which may suggest that other information from the whistleblower may also be corroborated.
Schiff also told Stephanopoulos that his committee has come to an agreement with the whistleblower and his or her attorneys to come before committee to provide firsthand information about what was detailed in the complaint. He added they expect to hear from the whistleblower "very soon," depending on Acting Director of National Intelligence Joseph Maguire completing the security clearance process for the whistleblower's lawyers.
"We're ready to hear from the whistleblower as soon as that is done," he said, referring to the security clearing process. "And we'll keep, obviously, riding shotgun to make sure the acting director doesn't delay in that clearance process."
He also defended himself from criticism over his characterization of the White House transcript of Trump and Zelenskiy’s July phone call during Maguire’s hearing on Thursday.
“You're right, the call speaks for itself,” he said. “It is plenty damning, but let's not pretend that this is really what the president is upset with me about."
During the hearing, Schiff compared the White House transcript of the call to a "classic mafia-like shakedown of a foreign leader."
(MORE: Articles of impeachment could come by Thanksgiving as Dems look to move quickly)"This is how a mafia boss talks," he said. "What have you done for us? We've done so much for you, but there's not much reciprocity."
In tweets Friday morning, the president accused Schiff of lying to Congress and called for him to "immediately resign."
ABC News' Ben Gittleson contributed to this report.