Democrats, including former Vice President Joseph R. Biden Jr., have previously accused Mr. McConnell of stopping the Obama administration from speaking out more forcefully against Russian interference. Mr. McConnell has long denied those allegations, pointing to a bipartisan letter that congressional leaders ultimately released in late September 2016.
The response to Russia’s meddling presented a difficult political calculus for Mr. McConnell: A public acknowledgment ahead of the election might have deterred Moscow and improved voters’ trust in the outcome, but none of that was assured, and it also could have cost Republicans the White House.
The full report from the committee, led by Senator Richard M. Burr, Republican of North Carolina, wavers on the impact that any high-level American government warning would have had on Russia’s campaign of election sabotage. The Kremlin’s operations continued even as the Obama administration began discussing them publicly, Senate investigators found.
“After the warnings, Russia continued its cyberactivity to include further public dissemination of stolen emails, clandestine social-media-based influence operations, and penetration of state voting infrastructure through Election Day 2016,” the report said.
Until the summer of 2016, administration officials viewed Russia’s cyberattacks as separate from its broader foreign policy goals and intelligence campaigns. That “bifurcated approach may have prevented the administration from seeing a more complete view of the threat,” the report said.
Even as of Oct. 1, 2016, administration officials had not reached a consensus that they would publicly attribute the meddling to Russia. Several issues divided the administration, like WikiLeaks’ role in disseminating Democratic emails stolen by Russian hackers and whether the organization should be considered a news outlet and granted First Amendment protections.
The scope of the Russian campaign was difficult to understand both inside the administration and on Capitol Hill, the report made clear. “Attribution is really hard,” Mr. King said. “It is not like there is a return address.”