WASHINGTON (AP) — Russia didn't have to lift a finger.

In the weeks before the U.S. presidential election, federal authorities warned that Russia or other foreign countries might spread false information about the results to discredit the legitimacy of the outcome.

Turns out, the loudest megaphone for that message belonged not to Russia but to President Donald Trump, who has trumpeted a blizzard of thoroughly debunked claims to proclaim that he, not President-elect Joe Biden, was the rightful winner.

The resulting chaos is consistent with longstanding Russian interests to sow discord in the United States and to chip away at the country's democratic foundations and standing on the world stage. If the 2016 election raised concerns about foreign interference in U.S. politics, the 2020 contest shows how Americans themselves, and their leaders, can be a powerful source of disinformation without other governments even needing to do the work.

“For quite a while at this point, the Kremlin has been able to essentially just use and amplify the content, the false and misleading and sensational, politically divisive content generated by political officials and American themselves" rather than create their own narratives and content, said former CIA officer Cindy Otis, vice president for analysis at the Alethea Group, which tracks disinformation.

U.S. officials had been on high alert for foreign interference heading into Nov. 3, especially after a presidential election four years earlier in which Russian intelligence officers hacked Democratic emails and Russian troll farms used social media to sway public opinion.

Public service announcements from the FBI and the Department of Homeland Security's cybersecurity arm warned of the ways Russia or other countries could interfere again, including by creating or altering websites after the election to spread false information about the results “in an attempt to discredit the electoral process and undermine confidence in U.S. democratic institutions.”

Yet many of the false claims about voting, elections and the candidates in the months and weeks ahead of the election — and in the days since — originated not from foreign actors eager to destabilize the U.S. but from domestic groups and Trump himself.

“Almost all of this is domestic,” said Alex Stamos, the director of the Stanford Internet Observatory and a member of the Election Integrity Partnership, a group of leading disinformation experts who studied online misinformation relating to the 2020 election.

Stamos said that while there were some small indications of foreign interference on social media, it amounted to “nothing that has been all that interesting” compared with the flood of claims shared by Americans themselves.

Though Russian hackers had targeted state and local networks in the weeks before the election, Election Day came and went without the feared attacks on voting infrastructure, and federal officials and other experts have said there is no evidence voting systems were compromised or any votes were lost or changed.

That's not to say Russia was entirely silent during the election, or in the immediate aftermath. For instance, English-language websites the U.S. government has linked to Russia have amplified stories suggesting voting problems or fraud.

Intelligence officials warned in August that Russia was engaged in a concerted effort to disparage Biden and singled out a Ukrainian parliamentarian who has met with Trump's personal lawyer, Rudy Giuliani.

Giuliani has been central to Trump's election attacks, arguing a Pennsylvania court case on Tuesday and appearing at a news conference on Thursday that was rife with debunked claims, including a fictitious story that a server hosting evidence of voting irregularities was in Germany.

Trump retweeted a post that criticized the news media for not more aggressively covering the news conference. More broadly, he has helped drive the spread of inaccurate information through a disinformation machine that relies on social media, conservative radio and television outlets and the amplification power of his millions of followers.

Zignal Labs, a San Francisco media intelligence firm, identified and tracked millions of social media posts about voting by mail in the months before the election and found huge spikes immediately following several of Trump’s tweets.

One example: On July 30, Trump tweeted misinformation about mail ballots three separate times, including stating without evidence that mail ballots would be an “easy way” for foreign adversaries to interfere, calling the process inaccurate and fraudulent and repeating a false distinction that absentee ballots are somehow more secure than mail ballots when both are treated the same.

Together, those three tweets were reposted by other users more than 100,000 times and liked more than 430,000 times — leading the spread of mail ballot misinformation that day and helping Trump dominate the online discussion the entire week, according to Zignal’s analysis.

Many of the false claims seen on Election Day originated with American voters themselves, whose posts about baseless allegations of voter fraud were then reposted to millions more people by Trump allies. That amplification allows isolated or misleading claims to spread more widely.

“You’re not talking about grassroots activity so much anymore,” Stamos said. “You’re talking about top-down activity that is facilitated by the ability of these folks to create these audiences.”

Researchers at Harvard University’s Berkman Klein Center for Internet & Society analyzed social media posts and news stories about voter fraud and determined that “Fox News and Donald Trump’s own campaign were far more influential in spreading false beliefs than Russian trolls or Facebook clickbait artists.”

One of the researchers, Harvard Law School professor Yochai Benkler, said that when his team looked at sudden increases in online chatter about voter fraud, they almost always followed a comment from Trump or top allies.

Justin Levitt, an election law expert at Loyola Law School, said that, unlike four years ago, “now we don’t need a foreign military unit to attack us. We have a chief executive doing exactly that” and working to spread disinformation.

“It’s even more dangerous this time,” he added, "than it was in 2016.”

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Klepper reported from Providence, Rhode Island. Associated Press writer Colleen Long in Washington contributed to this report.