WASHINGTON — Republicans on the House Intelligence Committee declared in a 250-page report on Friday that their yearlong investigation uncovered no evidence that the Trump campaign had aided Russia’s election meddling, only ill-advised contacts between campaign aides and Russian officials or their intermediaries.

The Republicans took aim at what they called the misjudgments of Democrats and others even as they sought to play down the seriousness of mistakes by or suspicions about Donald J. Trump’s presidential campaign. They faulted aides to Hillary Clinton for secretly paying for opposition research that included information from Russian sources, and castigated federal law enforcement and intelligence agencies for failing to counter Russian interference as well as for purported investigative abuses and allegedly damaging national security leaks.

In a nearly 100-page dissenting document, Democrats on the Intelligence Committee described the Republicans’ report as little more than a whitewash. The eagerness of Trump campaign aides to accept offers of Russian assistance, they said, suggests “a consciousness of wrongfulness, if not illegality.” The Democrats complained that the committee failed to pursue obvious leads, interview important witnesses or investigate crucial lines of inquiry.

The opposing conclusions closed a tumultuous chapter for a congressional committee that is charged with oversight of American spy agencies, but fractured into warring camps whose primary mission often seemed to be advancing their own political agendas. The results diminished hopes that Congress, which has mounted two similar investigations, is likely to get to the bottom of Russia’s attempts to influence the election.