Rep. Adam Schiff (Calif.), the top Democrat on the House intelligence committee, called Wednesday for an independent investigation into President Donald Trumps ties to Russia, arguing that the committees chairman, Rep. Devin Nunes (R-Calif.), cannot credibly conduct the probe.

[Nunes] actions simply raise enormous doubt about whether the committee can do its work, and I think that more than anything else Ive seen, this makes the most profound case for the formation of an independent commission, Schiff said during a news conference Wednesday.

His call came after Nunes, the leader of the congressional investigation into whether Trumps team colluded with Russian officials to interfere in the 2016 presidential election, said during a news conference Wednesday that some Trump surrogates were under surveillance during Obamas administration. Nunes visited the White House to brief the president on his findings before addressing the public.

That disclosure was news to Schiff, the congressman said.

I only learned about this the way you all did, he said.

Schiff said Nunes decision to brief Trump on the matter before discussing it with other members of the committee calls into question his credibility and ability to be a neutral investigator.

The chairman will need to decide whether he is the chairman of an independent investigation into conduct which includes allegations of potential coordination between the Trump campaign and the Russians, or if hes going to act as a surrogate of the White House, because he cannot do both, Schiff said.

I think the actions of today throw great doubt into the ability of both the chairman and the committee to conduct the investigation the way it ought to be conducted, he continued. I think it does underscore the importance of establishing an independent commission, a body that is fully independent of any political considerations, including those that may emanate from the White House.

Schiff said he expressed these grave concerns to Nunes himself.

Read more on Nunes earlier comments here.