Marie Harf said we could see a "constitutional crisis" if President Trump keeps meddling in the Russia investigation.

She agreed with former Attorney General Eric Holder's claim that Justice Department norms are being "eroded," and that Trump and his congressional supporters should not be requesting access to materials related to the ongoing probe.

"The norms about what governs ongoing investigations, about how the president interacts with the Department of Justice -- especially when he is part of this investigation -- he is eroding those norms," Harf said on "America's Newsroom."

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She said that Holder may not be the perfect messenger, but he is raising very valid and serious concerns about how Trump is involving himself in the investigation.

Harf, a former Obama administration official, said that all Americans -- regardless of political party -- should see that as a problem.

"If Donald Trump keeps meddling in the investigation, if he keeps putting his toes further into the water here, I do think we could get close to a constitutional crisis where [the] DOJ is being asked to do things that are wholly inappropriate," Harf said.

She said for legal and political reasons, Trump should keep his hands off the investigation and let it play out.

"That will give it more credibility in the end."

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