U.S. intelligence: Russia also hacked RNC -- but didn't disclose the data

One senior government official, who had been briefed on an F.B.I. investigation into the matter, said that while there were attempts to penetrate the Republican committee’s systems, they were not successful.

But the intelligence agencies’ conclusions that the hacking efforts were successful, which have been presented to President Obama and other senior officials, add a complex wrinkle to the question of what the Kremlin’s evolving objectives were in intervening in the American presidential election.

“We now have high confidence that they hacked the D.N.C. and the R.N.C., and conspicuously released no documents” from the Republican organization, one senior administration official said, referring to the Russians.

It is unclear how many files were stolen from the Republican committee; in some cases, investigators never get a clear picture. It is also far from clear that Russia’s original intent was to support Mr. Trump, and many intelligence officials — and former officials in Mrs. Clinton’s campaign — believe that the primary motive of the Russians was to simply disrupt the campaign and undercut confidence in the integrity of the vote.