An unusual question is capturing the attention of cyberspecialists, Russia experts and Democratic Party leaders in Philadelphia: Is Vladimir V. Putin trying to meddle in the American presidential election? Until Friday, that charge, with its eerie suggestion of a Kremlin conspiracy to aid Donald J. Trump, has been only whispered. But the release on Friday of some 20,000 stolen emails from the Democratic National Committee’s computer servers, many of them embarrassing to Democratic leaders, has intensified discussion of the role of Russian intelligence agencies in disrupting the 2016 campaign. The emails, released first by a supposed hacker and later by WikiLeaks, exposed the degree to which the Democratic apparatus favored Hillary Clinton over her primary rival, Senator Bernie Sanders of Vermont, and triggered the resignation of Debbie Wasserman Schultz, the party chairwoman, on the eve of the convention’s first day. Proving the source of a cyberattack is notoriously difficult. But researchers have concluded that the national committee was breached by two Russian intelligence agencies, which were the same attackers behind previous Russian cyberoperations at the White House, the State Department and the Joint Chiefs of Staff last year. And metadata from the released emails suggests that the documents passed through Russian computers. Though a hacker claimed responsibility for giving the emails to WikiLeaks, the same agencies are the prime suspects. Whether the thefts were ordered by Mr. Putin, or just carried out by apparatchiks who thought they might please him, is anyone’s guess.
On Sunday morning, the issue erupted, as Mrs. Clinton’s campaign manager, Robby Mook, argued on ABC’s “This Week” that the emails were leaked “by the Russians for the purpose of helping Donald Trump” citing “experts” but offering no other evidence. Mr. Mook also suggested that the Russians might have good reason to support Mr. Trump: The Republican nominee indicated in an interview with The New York Times last week that he might not back NATO nations if they came under attack from Russia — unless he was first convinced that the counties had made sufficient contributions to the Atlantic alliance.
It was a remarkable moment: Even at the height of the Cold War, it was hard to find a presidential campaign willing to charge that its rival was essentially secretly doing the bidding of a key American adversary. But the accusation is emerging as a theme of Mrs. Clinton’s campaign, as part of an attempt to portray Mr. Trump not only as an isolationist, but also as one who would go soft on confronting Russia as it threatens nations that have shown too much independence from Moscow or, in the case of Lithuania, Latvia and Estonia, joined NATO.
Mr. Trump has also said he would like to “get along with Russia” if he is elected, and complimented Mr. Putin, saying he is more of a leader than President Obama. Mr. Putin has in turn praised Mr. Trump. But Trump campaign officials on Sunday strongly rejected any connections between their candidate and efforts to undermine the Democrats.