U.S. intelligence agencies do not see Russia as capable of using cyberespionage to alter the outcome of Tuesday’s presidential election, but they have warned that Moscow may continue meddling after the voting has ended to sow doubts about the legitimacy of the result, U.S. officials said.

The assessment reflects widespread concern among U.S. spy agencies that a months-long campaign by Russia to rattle the mechanisms of American democracy will probably continue after polls close on one of the most polarizing races in recent history, extending and amplifying the political turbulence.

U.S. security officials have not ruled out Russian-sponsored disruption on Election Day. In recent weeks, officials at the Department of Homeland Security have collected evidence of apparent Russian “scanning” of state-run databases and computer voting systems. “Whether they were really trying hard to get in, it’s not clear,” a U.S. official said.

Still, the decentralized nature of U.S. polling would make it extraordinarily difficult to subvert a nationwide race. Instead, U.S. officials said it is more likely that Russia would use hacking tools to expose or fabricate signs of vote-rigging, aiming to delegitimize an election outcome that Republican candidate Donald Trump has said he may refuse to accept if he does not win.

“I think it’s correct to say the Russians don’t think they can dictate the outcome,” said Rep. Adam B. Schiff (Calif.), the top Democrat on the House Intelligence Committee. But even as votes are being tallied Tuesday, Schiff said, Russian intelligence services are likely to be “looking through their troves of hacked documents and seeing what they can release.”

At the third and final presidential debate, Democratic presidential nominee Hillary Clinton said Russian President Vladimir Putin would "rather have a puppet as president." (The Washington Post)

Whether Trump or Democratic nominee Hillary Clinton prevails, Schiff said, the United States “can expect a lot more of the same in terms of cyber-malevolence and influence” from Moscow.

[From ‘reset’ to ‘pause’: The real story behind Hillary Clinton’s feud with Vladimir Putin]

U.S. officials said there is still time for last-minute disruptions, even if the overall election appears relatively secure. Several officials said they fear that even an isolated operation that forces a voting system offline could erode confidence. Schiff and others said they remain worried that Moscow could dump doctored documents over the weekend that appear to expose illegality by the Clinton or Trump campaigns — disclosures designed to create confusion among voters that would be difficult to disprove before citizens cast their votes.

No forgeries have so far been identified among the thousands of files that U.S. officials believe were stolen by Russia and essentially laundered to the U.S. public and media through the WikiLeaks website.

The fact that Russia has so far refrained from altering documents or planting forgeries among the leaked emails is seen by some U.S. officials as potentially setting the stage for a more sinister plot. The media and public have come to see the WikiLeaks stockpiles as authentic, increasing the potential impact if Russia were to insert a deliberate but compelling falsehood.

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Russian President Vladi­mir Putin has repeatedly denied any Russian involvement in the ­election-related hacks. But those assertions have been dismissed by U.S. intelligence agencies and cybersecurity experts, with some saying that Russia engaged in sloppy tradecraft or seemed not terribly concerned about covering its tracks.

Anxiety about late-election vulnerabilities has factored into the Obama administration’s reluctance so far to retaliate against Russia.

The White House has opted against authorizing any countermeasures despite high confidence across U.S. spy agencies that Russia alone orchestrated the digital theft of thousands of sensitive documents posted online in recent months by WikiLeaks. The releases have included hacked files of the Democratic National Committee and emails of Clinton campaign chairman John Podesta, among others.

The White House has been weighing countermeasures for months but worried that retaliating before the election would give Moscow time to inflict more direct damage in the waning days of the campaign.

“Escalation in the cyber-realm can happen quickly,” a senior U.S. official said. Those urging restraint say they believe the Russian threat would be diminished after Election Day. Officials said the White House is also reluctant to take decisions on an escalation that could have profound implications for the next president.

U.S. officials said the options under consideration include kicking more suspected Russian intelligence officers out of the United States, imposing new economic sanctions against Russian entities tied to the alleged hacking and potentially launching cyberattacks on Russian computer systems. Obama used cyberweapons to hobble Iran’s nuclear program early in his first term but has been reluctant to go down that road again, aides say.

The administration’s decision could depend on what the Russians do in the coming days. An election-disrupting attack would probably trigger a more aggressive U.S. response, according to officials. U.S. officials say the stakes have been made clear to Moscow.

The election-related tensions are part of a broader escalation in the level of antagonism between the United States and its former Cold War adversary. The two countries are fighting a proxy war against each other in Syria, are competing for influence elsewhere in the Middle East and are at odds over Russian intervention in Ukraine.

The hack of the DNC was blamed on Russia by cybersecurity experts and U.S. officials the moment it was publicly disclosed in June. The administration formally went public with its case last month, issuing a statement from Director of National Intelligence James R. Clapper Jr. and Homeland Security Director Jeh Johnson concluding that intrusions were authorized by “Russia’s senior most officials.”

Even so, there is still disagreement among some agencies and analysts over Moscow’s objectives. The White House has maintained that it does not believe Russia’s operations have been aimed at delivering an election win for Trump, who has praised Putin and argued there is no evidence of Russian involvement in the hacks — a position at odds with what he has been told in classified briefings. The operations could be a more general effort to embarrass the United States and disrupt democratic institutions.

Clinton has said that Russia is seeking to ensure her defeat, a contention some U.S. intelligence officials say they believe is supported by the one-sided nature of the leaks. U.S. officials have speculated that Putin harbors personal animosity toward Clinton, believing that while serving as secretary of state she helped incite mass protests in Moscow that embarrassed the former KGB operative.

Even if there are no further election-related disruptions and Clinton emerges victorious, some U.S. officials believe that Russia has already accomplished many of its goals.

“They’ve weakened Secretary Clinton by dumping information from her campaign manager and others,” Schiff said. The leaks have exposed infighting between Clinton and her former Democratic opponent, Sen. Bernie Sanders of Vermont, forced the resignation of the DNC chief and — perhaps most importantly — cast Russia and its capacity to inflict damage as an ominous figure looming over the 2016 campaign.

“They enjoy being the subject of discussion in an American election,” Schiff said. “It enhances their prestige in a bizarre way that they’re considered a player. This is also their way of payback, and I think they are delighting in that.”

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