Rep. Jerrold Nadler (D-N.Y.), who is poised to take control of the House Judiciary Committee in January, said Sunday that he plans to call acting attorney general Matthew G. Whitaker as his first witness.

The hearing would focus on Whitaker’s “expressed hostility” to special counsel Robert S. Mueller III’s Russia investigation, which Nadler called “a real threat to the integrity of that investigation.” The Democrat said on CNN’s “State of the Union” that he is prepared to subpoena Whitaker if necessary.

Whitaker, who was named acting attorney general after Jeff Sessions stepped down last week, has been a controversial pick because of his vocal and written criticism of the Mueller probe. In his new role, Whitaker will supervise the investigation, absorbing the responsibility from Deputy Attorney General Rod J. Rosenstein, who was overseeing it only because Sessions had recused himself.

Despite his known conflicts, Whitaker reportedly has no intention of recusing himself.

Senate and House Democratic leaders sent a letter Sunday morning to the Justice Department’s ethics office outlining what they deemed Whitaker’s conflicts of interest and asking the office to review his past statements and make a recusal recommendation.

Rep. Adam B. Schiff (D-Calif.), the incoming chairman of the House Intelligence Committee, said Democrats will also determine whether Whitaker can be an impartial custodian of the Russia investigation.

“If he doesn’t recuse himself, if he has any involvement whatsoever in this Russia probe, we are going to find out whether he made commitments to the president about the probe, whether he is serving as a back channel to the president or his lawyers about the probe, whether he’s doing anything to interfere with the probe,” Schiff said during an interview on NBC’s “Meet the Press.”

“Mr. Whitaker needs to understand that he will be called to answer, and any role that he plays will be exposed to the public. We don’t want there to be any ambiguity about that,” Schiff continued.

Nadler, however, tempered expectations about seeking the impeachment of President Trump or Supreme Court Justice Brett M. Kavanaugh.

He said he saw “lots of potential” for impeaching Trump but that any move in that direction would be premature until the special counsel finished his investigation. Moreover, Nadler said, he wouldn’t move forward until there was enough evidence that, when presented to the American people, “a large fraction of people who voted for the president will grudgingly acknowledge to themselves and others that there was no choice but to impeach the president.”

Earlier on ABC’s “This Week,” he adopted a similarly moderate tone, saying he would be “reluctant” to put the country “through the trauma” of an impeachment without ascertaining the facts.

As for Kavanaugh, Nadler said on both shows that his committee would launch a probe into the FBI “not doing a proper investigation” of the sexual-misconduct accusations against Kavanaugh that date to his high school years.

Schiff said investigations shouldn’t get in the way of Democrats’ pledged legislative agenda that includes issues such as health care.

“The investigations are sexy. They’re interesting. You bring witnesses before the Klieg lights, people tune in,” he said. “The legislative process is less so. It’s much less dramatic. But, nonetheless, in terms of importance to the American people making sure that they can provide for their families, that they can get health care, they can keep their health care, that has to be priority number one.”

Frances Stead Sellers contributed to this report.