Former Director of National Intelligence James Clapper James Robert ClapperOn China, Biden is no Nixon — and no Trump The Hill's 12:30 Report - Speculation over Biden's running mate announcement Trump slams former intelligence officials to explain 'reluctance to embrace' agencies MORE said on Sunday that he believes there are “more shoes to drop” after an indictment stemming from special counsel Robert Mueller Robert (Bob) MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE’s probe into Russian interference in the 2016 election.

“Not addressed here is potential involvement of the Russian government, which we certainly saw through intelligence channels that the Russian government was masterminding this,” Clapper said Sunday on CNN's "State of the Union."

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The Department of Justice on Friday announced charges against 13 Russian nationals and three Russian organizations for allegedly attempting to interfere in the 2016 election. The indictment alleges the goal of the Russians was to support then-candidate Donald Trump and damage his opponent, Hillary Clinton Hillary Diane Rodham ClintonJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Momentum growing among Republicans for Supreme Court vote before Election Day Warning signs flash for Lindsey Graham in South Carolina MORE.

Clapper, who served as the director of national intelligence from 2010-2017, oversaw the intelligence community's report that concluded Russia conducted an influence campaign in an effort to aid then-candidate Donald Trump.

He said Sunday that the indictment validates that report.

“What was the big revelation to me was never before have we seen an effort like this mounted by the Russians,” Clapper said, noting it was more direct and aggressive than past efforts.

President Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE has repeatedly taken to Twitter following the indictment to argue that his campaign never colluded with Russia.

“We’re losing sight of what we’re going to do about the threat posed by Russians," Clapper said of Trump's response. "He never talks about that."