WASHINGTON — Partisan divisions and Republican congressional leaders’ reluctance to publicly acknowledge Russian election interference in 2016 contributed to a delayed response by the Obama administration in the midst of the presidential campaign, according to a Senate Intelligence Committee report released Thursday.

The report painted the Obama administration as moving too slowly and indecisively to address the interference or to counter it, and it cited the “heavily politicized environment” in American politics in 2016 as one factor preventing a more forceful response.

Though separate from its central findings, the mention of Republican congressional leaders’ role in forestalling a stronger response was notable for a report from a Republican-led committee.

Senator Mitch McConnell, Republican of Kentucky and the majority leader, reacted skeptically after receiving an intelligence briefing in September 2016 about the Russian interference, a former Obama administration official said in the report. “You security people should be careful that you’re not getting used,” Mr. McConnell told Lisa Monaco, the homeland security adviser under President Barack Obama at the time, according to the report.