And as social media companies more vigilantly monitor for foreign activity than they did in 2016, Russia has also adjusted its methods to evade detection. Rather than disseminate messages as widely as possible, as in 2016, Russian operatives are using private Facebook groups, posts on the online message board 4chan and closed chat rooms that are more difficult to monitor, according to intelligence officials.

Russia’s primary goal, according to several officials briefed on the intelligence who spoke on condition of anonymity to discuss sensitive information, is to foster a sense of chaos in the United States, though its motivations are under debate and difficult to decipher in the absence of high-level intelligence sources inside Moscow.

The direct effect of its interference on presidential politics is less clear, though some American officials said that Russia believed that acts of violence could bolster President Trump’s re-election bid if he could argue that a response to such an episode demanded continuity and that he represented a law-and-order approach.

The F.B.I. and other intelligence agencies declined to comment on specific Russian activities.

“We see Russia is willing to conduct more brazen and disruptive influence operations because of how it perceives its conflict with the West,” David Porter, a top agent on the F.B.I.’s Foreign Influence Task Force, said last month at an election security conference in Washington.

He added, “To put it simply, in this space, Russia wants to watch us tear ourselves apart.”

Because Russia is trying to amplify the messaging of existing groups, its interference is difficult for American officials to combat given First Amendment protections for speech. The government does have the legal authority to stop hate speech that explicitly advocates violence, and social media companies continue to take down accounts linked to Russian intelligence or disinformation groups.