FBI Director Christopher Wray on Thursday warned that Russia is interfering in the 2020 U.S. presidential elections with a steady stream of misinformation aimed at Democrat Joe Biden as well as sapping Americans’ confidence in the election process.

Moscow is also attempting to undercut what it sees as an anti-Russian U.S. establishment, the head of the Federal Bureau of Investigation told the Democratic-led House of Representatives’ Homeland Security committee.

He said his biggest concern is a “steady drumbeat of misinformation” that he said he feared could undermine confidence in the result of the 2020 election.

Wray’s testimony follows an Aug. 7 warning by the director of the National Counterintelligence and Security Center that Russia, China and Iran were all trying to interfere in the Nov. 3 election.

Multiple reviews by U.S. intelligence agencies have concluded that Russia acted to boost now-President Donald Trump’s 2016 campaign and undermine his Democratic rival Hillary Clinton. The Republican president has long bristled at that finding, which Russia denies.

Trump himself has repeatedly and without evidence questioned the increased use of mail-in ballots, a long established method of voting in the United States which are expected to see a surge in use due to the coronavirus. On Thursday Trump wrote on Twitter, without evidence, that they could make it impossible to know the election’s true outcome.

Regarding China, Wray said that the FBI is so active in monitoring Chinese efforts to acquire U.S. technology and other sensitive information that it is opening a new counterintelligence investigation related to China “every 10 hours.”

Wray said the FBI is conducting multiple investigations into violent domestic extremists following months of street protests against racism and police brutality. He said the largest “chunk” of investigations were into white supremacist groups.