Hillary ClintonHillary Diane Rodham ClintonSuper PACs release ad campaign hitting Vance over past comments on Trump I voted for Trump in 2020 — he proved to be the ultimate RINO in 2021 Neera Tanden tapped as White House staff secretary 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 SandersSanders on Medicare expansion in spending package: 'Its not coming out' Briahna Joy Gray: Biden must keep progressive promises or risk losing midterms Overnight Health Care — Presented by Carequest — Study finds Pfizer vaccine almost 91 percent effective for 5 to 11 year olds 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 TrumpGrant Woods, longtime friend of McCain and former Arizona AG, dies at 67 Super PACs release ad campaign hitting Vance over past comments on Trump Glasgow summit raises stakes for Biden deal 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.