Democratic presidential nominee Hillary ClintonHillary Diane Rodham ClintonDemocrats worry negative images are defining White House Heller won't say if Biden won election Whitmer trailing GOP challenger by 6 points in Michigan governor race: poll MORE's campaign manager, Robby Mook, on Sunday said there were "real questions" about Donald TrumpDonald TrumpGraham says he hopes that Trump runs again Trump says Stacey Abrams 'might be better than existing governor' Kemp Executive privilege fight poses hurdles for Trump MORE's connections to Russia following the departure of his former campaign manager, Paul Manafort.

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"We now need Donald Trump to explain to us the extend to which the hand of the Kremlin is at the core of his own campaign," Mook said on ABC's "This Week."

"There's a web of financial interests that have not been disclosed, and there are real questions being raised about whether Donald Trump himself is just a puppet for the Kremlin."

Manafort resigned last week amid a campaign shake-up.

Before his departure, he was under fire over work he did for a pro-Russian political party in Ukraine.

Mook said there is a web of financial ties to the Russians that Trump, the Republican presidential nominee, has not yet disclosed. He cited Trump's recent statements about Russia.

"We've seen, over the last few weeks, him parroting [Russian President] Vladimir Putin in his own remarks," Mook said.

"We saw the Republican Party platform change. We saw Donald Trump talk about leaving NATO and leaving our Eastern European allies vulnerable to a Russian attack."

Mook also called out Manafort.

"The gentleman he brought with him to his security briefing just last week is someone who's on the payroll of the Russia Times, which is basically a propaganda arm of the Kremlin," Mook said.

There are "a lot of questions" regarding Trump's ties, Mook said.

"We need Donald Trump to disclose all of his financial ties," Mook said, "and whether his advisers are having meetings with the Kremlin."