Clinton Campaign Manager: Prospect of More DNC Emails Being Released Was ‘Concerning’

— -- Hillary Clinton's campaign manager Robby Mook said on "Good Morning America" that he was concerned an "aggressive regime" like Russian President Vladimir Putin's could be trying to "infiltrate the system of the Democratic Party" and also "influence the outcome of the election."

Mook was responding to a question this morning regarding the email hack from WikiLeaks that showed that several staff members of the Democratic National Committee were biased against Sen. Bernie Sanders during the campaign primary. Michael Buratowski, a cyber analyst with the firm that investigated the hack, told ABC News on Monday he's "very confident" that Russian actors were behind the cyber attack. According to Buratowski, the hackers were using Russian internet addresses and typing on keyboards configured in Cyrillic.

Mook added that it was "also very troubling" that Republican presidential nominee Donald Trump appeared to be pushing for a pro-Russian platform. Trump has praised Putin and recently declared that, if he becomes president, the United States would defend fellow NATO countries only if the nations in question were contributing their fair share to the alliance’s budget – a stance that would bode well for Russia.

"Obviously, this is a concerning situation," Mook said.

Trump’s campaign chairman Paul Manafort has called the accusations that Trump colluded with Russia in the DNC email hack “absurd.”

Mook was optimistic Democrats would come together in support of Clinton despite the email controversy, which has triggered protests and forced Democratic National Committee chairwoman Debbie Wasserman Schultz to resign from her post, effective later this week.

Although supporters of Sanders protested against Clinton’s campaign at the convention last night, Mook noted that Sanders still gave a “rousing” endorsement along with other Democratic officials. At last week's Republican convention, Sen. Ted Cruz refused to endorse Trump and Ohio Gov. John Kasich was absent from the event.

“The contrast between our convention and the Republican’s could not be greater," Mook said. “We are working hard to unify this party.”