Under Mr. Putin, Russian intelligence has long sought to stir turmoil among around the world. The United States and key allies on Thursday accused Russian military intelligence, the group responsible for much of the 2016 election interference in the United States, of a cyberattack on neighboring Georgia that took out websites and television broadcasts.

The Russians have been preparing — and experimenting — for the 2020 election, undeterred by American efforts to thwart them but aware that they needed a new playbook of as-yet-undetectable methods, United States officials said.

They have made more creative use of Facebook and other social media. Rather than impersonating Americans as they did in 2016, Russian operatives are working to get Americans to repeat disinformation, the officials said. That strategy gets around social media companies’ rules that prohibit “inauthentic speech.”

And the Russians are working from servers in the United States, rather than abroad, knowing that American intelligence agencies are prohibited from operating inside the country. (The F.B.I. and the Department of Homeland Security are allowed to do so with aid from the intelligence agencies.)

Russian hackers have also infiltrated Iran’s cyberwarfare unit, perhaps with the intent of launching attacks that would look like they were coming from Tehran, the National Security Agency has warned.

Some officials believe that foreign powers, possibly including Russia, could use ransomware attacks, like those that have debilitated some local governments, to damage or interfere with voting systems or registration databases.

Still, much of the Russian aim is similar to its 2016 interference, officials said: search for issues that stir controversy in the United States and use various methods to stoke division.

One of Moscow’s main goals is to undermine confidence in American election systems, intelligence officials have told lawmakers, seeking to sow doubts over close elections and recounts. American officials have said they want to maintain confidence in the country’s voting systems, so confronting those Russian efforts is difficult.

Both Republicans and Democrats asked the intelligence agencies to hand over the underlying material that prompted their conclusion that Russia again is favoring Mr. Trump’s election.

Although the intelligence conclusion that Russia is trying to interfere in the 2020 Democratic primaries is new, in the 2019 report of the special counsel, Robert S. Mueller III, there is a reference to Russian desires to help Mr. Sanders in his presidential primary campaign against Hillary Clinton in 2016. The report quoted internal documents from the Internet Research Agency, a troll factory sponsored by Russian intelligence, in an order to its operatives: “Use any opportunity to criticize Hillary and the rest except for Sanders and Trump — we support them.”

How soon the House committee might get that information is not clear. Since the impeachment inquiry, tensions have risen between the Office of the Director of National Intelligence and the committee. As officials navigate the disputes, the intelligence agencies have slowed the amount of material they provide to the House, officials said. The agencies are required by law to regularly brief Congress on threats.

While Republicans have long been critical of the Obama administration for not doing enough to track and deter Russian interference in 2016, current and former intelligence officials said the party is at risk of making a similar mistake now. Mr. Trump has been reluctant to even hear about election interference, and Republicans dislike discussing it publicly.

The aftermath of last week’s briefing prompted some intelligence officials to voice concerns that the White House will dismantle a key election security effort by Dan Coats, the former director of national intelligence: the establishment of an election interference czar. Ms. Pierson has held the post since last summer.

And some current and former intelligence officials expressed fears that Mr. Grenell may have been put in place explicitly to slow the pace of information on election interference to Congress. The revelations about Mr. Trump’s confrontation with Mr. Maguire raised new concerns about Mr. Grenell’s appointment, said the Democratic House committee official, who added that the upcoming election could be more vulnerable to foreign interference.

Mr. Trump, former officials have said, is typically uninterested in election interference briefings, and Mr. Grenell might see it as unwise to emphasize such intelligence with the president.

“The biggest concern I would have is if the intelligence community was not forthcoming and not providing the analysis in the run-up to the next election,” said Andrea Kendall-Taylor, a former intelligence official now with the Center for a New American Security. “It is really concerning that this is happening in the run-up to an election.”

“Trump is trying to whitewash or rewrite the narrative about Russia’s involvement in the election,” she said. “Grenell’s appointment suggests he is really serious about that.”

The acting deputy to Mr. Maguire, Andrew P. Hallman, will step down on Friday, officials said, paving the way for Mr. Grenell to put in place his own management team. Mr. Hallman was the intelligence office’s principal executive, but since the resignation in August of the previous deputy, Sue Gordon, he has been performing the duties of that post.

Mr. Maguire is planning to leave government, according to an American official.

Adam Goldman, Julian E. Barnes and Nicholas Fandos reported from Washington, and Maggie Haberman from New York. Eric Schmitt and David E. Sanger contributed reporting from Washington.