The leader of the National Security Agency says there shouldn’t be “any doubt in anybody’s mind” that there was “a conscious effort by a nation-state” to sway the result of the 2016 presidential election.

Adm. Michael Rogers, who leads both the NSA and US Cyber Command, made the comments during a conference presented by The Wall Street Journal in response to a question about WikiLeaks’ release of nearly 20,000 internal emails from the Democratic National Committee.

“There shouldn’t be any doubt in anybody’s mind,” Rogers said. “This was not something that was done casually. This was not something that was done by chance. This was not a target that was selected purely arbitrarily. This was a conscious effort by a nation-state to attempt to achieve a specific effect.”

Rogers did not specify the nation-state or the specific effect, though US intelligence officials say they suspect Russia provided the emails to WikiLeaks after hackers stole them from DNC servers and the personal email account of Hillary Clinton’s campaign manager, John Podesta.

At least two different hacker groups associated with the Russian government were found inside the networks of the DNC over the past year reading emails, chats, and downloading private documents. Many of those files were later released by WikiLeaks.

The hack, which was investigated by the FBI and the cybersecurity firm Crowdstrike, was linked to Russia through a lengthy technical analysis, which was detailed on the firm’s blog. Former NSA research scientist Dave Aitel, who now leads another cybersecurity firm, has called the analysis “pretty dead on.”

The hack of Podesta’s private Gmail address was traced by cybersecurity researchers to hackers with Russia’s foreign intelligence service, the GRU, because the group made an error during its campaign of “spear phishing” targets – tricking them into clicking on malicious links or give up their passwords. The researchers found that the group had targeted more than 100 email addresses that were associated with the Clinton campaign, according to The New York Times.

The Obama administration in October publicly accused Russia of being behind the hacks.

“The US intelligence community is confident that the Russian Government directed the recent compromises of emails,” reads a statement from the Department of Homeland Security. “These thefts and disclosures are intended to interfere with the US election process.”

Republican Sen. Lindsey Graham of South Carolina said on Tuesday that he wants the Senate to open an investigation into whether the Russian government meddled in the US election. Russian President Vladimir Putin has repeatedly denied his country was behind the hacks.