Hillary ClintonHillary Diane Rodham ClintonClose the avenues of foreign meddling Pelosi planned on retiring until Trump won election: report Pence autobiography coming from Simon & Schuster MORE's campaign manager on Sunday questioned whether Russia is behind the leaked emails that show Democratic Party officials privately planned how to undermine the presidential campaign of Sen. Bernie SandersBernie SandersBiden's policies are playing into Trump's hands Hillicon Valley: Amazon wins union election — says 'our employees made the choice' On The Money: Biden .5T budget proposes major hike in social programs | GOP bashes border, policing provisions MORE (I-Vt.). 

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"What's disturbing about this entire situation is that experts are telling us that Russian state actors broke into the DNC, took all those emails and are now leaking them out through these websites," Robby Mook said on ABC's "This Week," referring to the Democratic National Committee. 

"It's troubling that some experts are telling us this was done by the Russians for the purpose of helping Donald TrumpDonald TrumpGaetz was denied meeting with Trump: CNN Federal Reserve chair: Economy would have been 'so much worse' without COVID-19 relief bills Police in California city declare unlawful assembly amid 'white lives matter' protest MORE." 

Mook also criticized an email that appears to show DNC Chief Financial Officer Brad Marshall questioning Sanders's religion. 

"Nobody in politics should be attacked for their religion, ever,"  Mook said, noting that Marshall apologized for the email.  

In the emails leaked Friday by WikiLeaks, Marshall wrote: “It might may no difference, but for KY and WVA can we get someone to ask his belief. Does he believe in a God. He had skated on saying he has a Jewish heritage. I think I read he is an atheist. This could make several points difference with my peeps. My Southern Baptist peeps would draw a big difference between a Jew and an atheist."

The leak comes ahead of this week's Democratic National Convention in Philadelphia, where Clinton will accept the party's nomination for president.  

"I think the DNC needs to get to the bottom of the facts and take appropriate action on these emails," Mook said Sunday.