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 on Sunday that impeachment "may be the only remedy" if President Trump asked the leader of Ukraine to find dirt on former Vice President Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE, a 2020 Democratic White House hopeful.

Schiff, who has been reluctant to push for impeachment, said on CNN's "State of the Union" that it "may be that we do have to move forward with that extraordinary remedy" if Trump sought information on Biden.

"[I] want the country to understand this is the last resort," Schiff said.

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"The president is pushing us down this road," he added.

Schiff said he has demanded a copy of a whistleblower's complaint reportedly centered on the call between Trump and a foreign leader in order to release its contents.

The Wall Street Journal reported the president asked Ukraine's leader to investigate Biden's son's past dealings in the country. No evidence has emerged to suggest Biden acted with his son's interests in mind with regard to his dealings with Ukraine.

Trump has said that he won't discuss his call with Ukraine's president, and the White House refuses to release a transcript or the whistleblower complaint.

"Clearly, the president is afraid for the public to see either one of those things," Schiff said on Sunday, adding that House Democrats will make sure the public does see them.

The president's 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 had previously admitted having called Ukraine about investigating Biden, but Schiff said on Sunday the allegations over Trump's direct call are more alarming.

"It's one thing when done by the court jester, another when done by the king," Schiff said.