WASHINGTON — With congressional elections just a year away, lawmakers are scrambling to stop Russia from hacking state election systems and using social media to create chaos and uncertainty among voters.

But Congress may be stymied by its reluctance to regulate private tech companies and by states' traditional aversion to any federal control over their elections, analysts say.

The burden on the three congressional committees conducting investigations into Russian meddling has become much greater than simply trying to prevent Kremlin-linked groups from stealing campaign emails, as they allegedly did last year in cyber attacks against the Democratic National Committee and Hillary Clinton's presidential campaign.

Recent revelations about the extent of Russian efforts — both past and present — to spread disinformation via Facebook, Twitter and other social media sites underscores just how big a challenge Congress is facing as it heads toward the 2018 midterm elections.

"Congress may have begun its investigation looking for a nice, neat smoking keyboard," said Eric Herzik, chairman of the political science department at the University of Nevada, Reno. "But this is not a case where you can call the vendor and get a patch to plug a security hole. This has become incredibly complicated."

Adding to lawmakers' alarm: Federal officials recently told election officials in 21 states that hackers possibly connected to Russia targeted their election systems last year. Leaders of the Senate Intelligence Committee warned Wednesday that they expect the Russians to try again in the 2018 congressional elections, the 2020 presidential election and possibly even this year in the Virginia governor's race.

"We need to be on guard," said Intelligence Vice Chairman Mark Warner, D-Va.

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The biggest risk, analysts say, is not that the Russians will help one party's candidates defeat the other's but that they will succeed in causing Americans to doubt the legitimacy of election results.

"I don't think the Russians have a favorite political party," said Jack Pitney, a politics professor at Claremont McKenna College in California. "They do have a preference for chaos and division."

A report released in January by the U.S. Intelligence Community concluded that Russia interfered in last year's election to boost Donald Trump and hurt Clinton.

"But their bigger goal is to disrupt the American political process and sow distrust and discontent," Herzik said.

Facebook recently turned over more than 3,000 suspicious ads to the House Intelligence Committee. The ads were purchased by an organization that Facebook said was connected to Russian intelligence services during the 2016 election.

"These ads ... help demonstrate how Russia employed sophisticated measures to push disinformation and propaganda to millions of Americans online during the election, in order to sow discord and chaos, and divide us from one another," said Rep. Adam Schiff of California, the committee's senior Democrat.

The House panel, along with the Senate Intelligence Committee and the Senate Judiciary Committee, is investigating Russian interference in last year's presidential election and possible collusion between the Trump campaign and Russian officials.

Both the House and Senate Intelligence committees are planning public hearings in the next few weeks with Facebook and other social media companies to examine how Russia exploited social media.

"If you see an ad on a social media site, Americans should know whether the source of that ad was a foreign entity," Warner told reporters. "And if you see something trending, you should know whether that trending is generated by real individuals or bots or falsely identified accounts."

Sen. James Lankford, R-Okla., a member of both the Senate Intelligence and Homeland Security committees, said that Russians have been weighing in on Twitter on both sides of the recent dispute between President Trump and the NFL over whether players should be fired for refusing to stand during the national anthem.

"We watched ... the Russians and their troll farms and their Internet folks start hash-tagging out 'take a knee' and also hash-tagging out 'boycott NFL,' " Lankford said at a hearing of the Homeland Security and Governmental Affairs Committee.

The Russians' goal, Lankford said, was "to try to just raise the noise level in America and to make a big issue seem like an even bigger issue as they are trying to push divisiveness in the country."

"We will see that again in our election," he said.

There is little Congress can do to control what happens on social media other than push tech companies to better police themselves and identify who is buying ads or pushing out false information on their sites, Pitney said.

"It's a classic case of congressional pressure as a way of increasing self-regulation by the companies," the professor said. "But it's probably impossible to stop this entirely."

Henry Farrell, a professor of political science and international affairs at George Washington University, said he is more concerned about Russian efforts to hack state elections' systems.

"I think the threat to election machines is substantially more significant," he said.

Lawmakers have been pressing the Department of Homeland Security about what federal officials are doing to prevent Russia or other foreign governments from hacking state election systems next year.

Acting Homeland Security Secretary Elaine Duke told the Senate Homeland Security Committee recently that her agency has the resources it needs to do on-site assessments of election security for all the states that request it before the 2018 election.

"Not all states have requested it, and I think there is still an issue with some states on whether they want that federal involvement," Duke told the senators. "But we do have the resources."

States pride themselves on local control of their election systems and say that one of the reasons it's hard to disrupt voting in the U.S. is because there is no central, national election database to hack.

It may take a successful cyber attack against a state to change their view of federal help, Farrell said.

"But at the moment, it is very, very difficult politically for Congress to do much," he said.