Hillary Clinton is seen aboard the campaign bus in Cleveland on the third day of a bus tour through Pennsylvania and Ohio.

July 31, 2016 Hillary Clinton is seen aboard the campaign bus in Cleveland on the third day of a bus tour through Pennsylvania and Ohio. Melina Mara/The Washington Post

The former secretary of state, senator and first lady is the Democratic nominee for president.

The former secretary of state clinched the number of delegates needed to be the Democratic presidential nominee.

The former secretary of state clinched the number of delegates needed to be the Democratic presidential nominee.

A top official with Hillary Clinton’s campaign on Sunday accused the Russian government of orchestrating the release of damaging Democratic Party records to help the campaign of Republican Donald Trump — and some cybersecurity experts agree.

The extraordinary charge came as some national security officials have been growing increasingly concerned about possible efforts by Russia to meddle in the election, according to several individuals familiar with the situation.

Late last week, hours before the records were released by the website WikiLeaks, the White House convened a high-level security meeting to discuss reports that Russia had hacked into systems at the Democratic National Committee.

Although other experts remain skeptical of a Russian role, the hacking incident has caused alarm within the Clinton campaign and also in the national security arena. Officials from various intelligence and defense agencies, including the National Security Council, the Department of Defense, the FBI and the Department of Homeland Security, attended the White House meeting Thursday, on the eve of the email release.

If the accusation is true, it would be the first time the Russians have actively tried to influence an election in this manner, analysts said.

Debbie Wasserman Schultz, the chairwoman of the Democratic National Committee said she will resign this week in the aftermath of the release of thousands of internal email exchanges among Democratic officials. (Thomas Johnson,Monica Akhtar/The Washington Post)

Clinton’s campaign chief, Robby Mook, told ABC News on Sunday that “experts are telling us that Russian state actors broke in to the DNC, took all these emails and now are leaking them out through these Web sites. . . . It’s troubling that some experts are now telling us that this was done by the Russians for the purpose of helping Donald Trump.”

Trump campaign officials rejected the suggestion as absurd.

The most sensational revelation so far in the emails is that officials at the supposedly impartial DNC were in fact helping Clinton during the primary. One email written May 5 to Luis Miranda, the national communications director for the DNC, from another party official suggests that the party could help Clinton by raising questions about Sanders’s faith. Other emails generally disparaged Sanders and indicated a preference for Clinton.

The emails have infuriated Sanders supporters, who have repeatedly accused the DNC of improperly helping the Clinton campaign during the primary. The episode prompted the resignation Sunday of DNC Chairwoman Debbie Wasserman Schultz.

“They said they were neutral, which we knew not to be true,” said Sanders campaign manager Jeff Weaver. “Now we have evidence in black and white that they were trying to put out negative stories about Bernie Sanders. People are very angry about these leaks, and rightfully so. There’s no doubt about that.”

Beyond Mook, DNC and Clinton campaign officials have not responded to requests for comment Friday as reporters and unnerved campaign staff tried to assess the damage caused by the release, which comes just as the party holds a nominating convention in Philadelphia designed to project unity after a bitter primary season.

The emails were released Friday on Twitter by WikiLeaks. The document dump follows a report last month by The Washington Post that Russian government hackers had penetrated the computer network of the DNC, gaining access to an entire database of opposition research, among other material.

The Post's Ellen Nakashima goes over the events, and discusses the two hacker groups responsible. (Jhaan Elker/The Washington Post)

Other emails offered details of perks provided to party donors attending the convention and other events involving Democratic officials.

On Sunday, Mook and others noted that Trump has taken positions in the campaign that seem to align with those held by Russian President Vladi­mir Putin. He cited Trump’s recent statement on NATO — that he might not provide assistance to member states that hadn’t contributed their financial share — as a sign that the Republican nominee is taking positions favorable to Putin.

“I think when you put all this together, it’s a disturbing picture and voters need to reflect on that,” Mook told CNN in an interview Sunday.

Trump’s campaign chairman, Paul Manafort, flatly denied the insinuation, calling Mook’s comments “pure obfuscation” on ABC’s “This Week.”

“What they don’t want to talk about is what’s in those emails,” Manafort said.

Last month, the forensic firm CrowdStrike said two competing Russian intelligence hacker groups penetrated the DNC’s computers. In the past 24 hours, cybersecurity experts have said that the email cache released by WikiLeaks on Friday appears to have been given to the anti-secrecy group by Russian intelligence.

Thomas Rid, a professor at King’s College London, said in an interview that in a private chat on Twitter on Saturday, he communicated with the entity that claimed to have released the email cache to WikiLeaks.

The party, which calls itself Guccifer2, last month claimed responsibility for the DNC hack. Several independent analysts have concluded that Guccifer2, who claimed to be Romanian, is likely linked to Russia.

“We’ve been looking at this very closely from both the technical and non-technical spheres,” said Richard Barger, chief information officer for ThreatConnect, a cyber-intelligence software firm. “Based on our analysis, we strongly feel Guccifer2 is linked to a Russian information operations campaign and is not the independent Romanian hacker that he claims to be.”

The apparent link to Russian intelligence raises troubling implications for U.S. foreign relations and national security. Russia has not to date tried to interfere in U.S. elections, analysts say. But if this is a deliberate effort by the Kremlin to meddle, it is worrisome, they say.

Michael G. Vickers, who served as undersecretary of defense for intelligence from 2011 to 2015, said an effort by the Russians to release intelligence in advance of a U.S. election is likely unprecedented.

“What is really new here is the attempt to influence the politics of the United States. That is the problem,” he said.

Vickers said that the Russians have attempted to influence elections in states closer to their border but that seeking to do so in the United States would represent a historic and significant change, even in an era when Russian intelligence gathering has become more aggressive.

Because he is no longer in government service, Vickers said he had no direct knowledge of the forensic evidence in the DNC email case. However, he said that “people who have looked at it have said it looks like groups that have been tied to Russian intelligence.”

Fiona Hill, a former Russia expert on the National Intelligence Council, said putting the emails out on WikiLeaks for the world to see is consistent with her view of the modus operandi of Putin and Russian intelligence.

“They’re doing what they do best,” said Hill, now a Brookings Institution senior fellow. “They would not be doing their jobs as intelligence officers if they were not trying to outsmart their main opponent and to have influence on their politics.”

But, Rid pointed out, “what we don’t know is whether this is a top-down order or not.”

Russian Embassy officials did not respond to a request for comment Sunday. In the past, Russian officials denied any involvement with the hack.

“I completely rule out a possibility that the [Russian] government or the government bodies have been involved in this,” ­Dmitry Peskov, the Kremlin’s spokesman, told the Reuters news agency in Moscow.

Eugene Rumer, a former analyst on the National Intelligence Council who left in 2014, said that, if the accusation is true, “the implication is troublesome, no question about it.”

One possibility is the Russians are trying in some way to influence the election outcome and perhaps promote Trump by embarrassing Clinton. If that is the case, Rumer said, “it suggests the kind of misunderstanding of American domestic politics. To think that they can affect the outcome in a country of over 300 million people, with billions spent on electoral campaigns, in a country where there is free media”

Another possibility is that this is part of an information warfare campaign that involves the release of compromising materials, or what in Russian is called kompromat. “You release dirt on me. I release dirt on you,” Rumer said.

The Russians have made clear that they believe the United States is behind the release of the Panama Papers, which include material embarrassing to Putin. They are upset about the Olympics doping scandal, which they also believe was fomented by Western intelligence agencies.

“Whoever is behind this may feel, well, you people try to tarnish our leader, we’re going to dump this and show that your politics is no better than ours,” Rumer said.

One U.S. official, who like others interviewed for this report spoke on the condition of anonymity, said the email dump “would be the worst possible way to influence an election. It just seems a little clumsy. It just seems a very odd way of going about it.”

WikiLeaks is nonetheless an ideal venue for gaining exposure, other analysts say. The site, cofounded in 2006 by Julian ­Assange, promotes itself as an anti-secrecy organization and promises leakers’ anonymity.

“If you’re the Russians and you want to leak information for maximal effect, WikiLeaks is a great platform for that,” said one analyst, who spoke on the condition of anonymity because his work involves studying Russian intelligence and he did not want to draw attention to himself.

Russia has intervened in other countries’ elections. For instance, in Ukraine in 2004, a Russian hacker group calling itself Cyber Berkut claimed it hacked and disabled the electronic vote-counting system of the Ukraine central election commission three days before the presidential election. The election followed the toppling of a pro-Moscow leader, a move that set off Russia’s invasion and annexation of Crimea.

Analysts have attributed the hack to the GRU, one of the same Russian military intelligence services said to have hacked the DNC. They said that the agency created Cyber Berkut, which portrayed itself as an independent hacktivist group but in reality was used to further Moscow’s political interests in Ukraine.

Likewise, French authorities say a cyberattack last year on the French television network TV5Monde was carried out by Russian hackers. A group posing as being linked to the Islamic State and calling itself “Cyber Caliphate” posted jihadist propaganda on the station’s website — an apparent effort to deflect suspicion away from Russia — and plunged the network’s TV channels into darkness. Again, it was the GRU that was said to be behind the attack, the French authorities said. Some analysts said they believed the attack was Russian retaliation against France for backing out of a deal to sell helicopter carriers to Russia because of Moscow’s aggression in Ukraine.

Within 24 hours of the news breaking of the Russian hack of the DNC, files that purported to be from the servers began to appear online. Guccifer2 claimed credit for the hack and portrayed itself as independent of Russia. But a number of independent experts pointed to evidence that Guccifer2 appeared to be linked to Russia and said they believed Guccifer2 was trying to deflect blame from Russia.

The Post has previously reported that Trump has had a long-standing interest in Russia. In addition, The Post found that Manafort has multimillion-dollar financial ties to oligarchs in the former Soviet Union.