WASHINGTON — The C.I.A. told senior lawmakers in classified briefings last summer that it had information indicating that Russia was working to help elect Donald J. Trump president, a finding that did not emerge publicly until after Mr. Trump’s victory months later, former government officials say.
The briefings indicate that intelligence officials had evidence of Russia’s intentions to help Mr. Trump much earlier in the presidential campaign than previously thought. The briefings also reveal a critical split last summer between the C.I.A. and counterparts at the F.B.I., where a number of senior officials continued to believe through last fall that Russia’s cyberattacks were aimed primarily at disrupting America’s political system, and not at getting Mr. Trump elected, according to interviews.
The former officials said that in late August — 10 weeks before the election — John O. Brennan, then the C.I.A. director, was so concerned about increasing evidence of Russia’s election meddling that he began a series of urgent, individual briefings for eight top members of Congress, some of them on secure phone lines while they were on their summer break.
It is unclear what new intelligence might have prompted the classified briefings. But with concerns growing both internally and publicly at the time about a significant Russian breach of the Democratic National Committee, the C.I.A. began seeing signs of possible connections to the Trump campaign, the officials said. By the campaign’s final weeks, Congress and the intelligence agencies were racing to understand the scope of the Russia threat.
In an Aug. 25 briefing for Harry Reid, then the top Democrat in the Senate, Mr. Brennan indicated that Russia’s hackings appeared aimed at helping Mr. Trump win the November election, according to two former officials with knowledge of the briefing.
The officials said Mr. Brennan also indicated that unnamed advisers to Mr. Trump might be working with the Russians to interfere in the election. The F.B.I. and two congressional committees are now investigating that claim, focusing on possible communications and financial dealings between Russian affiliates and a handful of former advisers to Mr. Trump. So far, no proof of collusion has emerged publicly.
Mr. Trump has rejected any suggestion of a Russian connection as “ridiculous” and “fake news.” The White House has also sought to redirect the focus from the investigation and toward what Mr. Trump has said, with no evidence, was President Barack Obama’s wiretapping of phones in Trump Tower during the presidential campaign.
The C.I.A. and the F.B.I. declined to comment for this article, as did Mr. Brennan and senior lawmakers who were part of the summer briefings.
In the August briefing for Mr. Reid, the two former officials said, Mr. Brennan indicated that the C.I.A., focused on foreign intelligence, was limited in its legal ability to investigate possible connections to Mr. Trump. The officials said Mr. Brennan told Mr. Reid that the F.B.I., in charge of domestic intelligence, would have to lead the way.
Days later, Mr. Reid wrote to James B. Comey, director of the F.B.I. Without mentioning the C.I.A. briefing, Mr. Reid told Mr. Comey that he had “recently become concerned” that Russia’s interference was “more extensive than widely known.”
In his letter, the senator cited what he called mounting evidence “of a direct connection between the Russian government and Donald Trump’s presidential campaign” and said it was crucial for the F.B.I. to “use every resource available” to investigate.
Unknown to Mr. Reid, the F.B.I. had already opened a counterintelligence inquiry a month before, in late July, to examine possible links between Russia and people tied to the Trump campaign. But its existence was kept secret even from members of Congress.
Well into the fall, law enforcement officials said that the F.B.I. — including the bureau’s intelligence analysts — had not found any conclusive or direct link between Mr. Trump and the Russian government, as The New York Times reported on Oct. 31.
But as the election approached and new batches of hacked Democratic emails poured out, some F.B.I. officials began to change their view about Russia’s intentions and eventually came to believe, as the C.I.A. had months earlier, that Moscow was trying to help get Mr. Trump elected, officials said.
It was not until early December, a month after the election, that it became publicly known in news reports that the C.I.A. had concluded that Moscow’s motivation was to get Mr. Trump elected.
In January, intelligence officials publicly released a declassified version of their findings, concluding that President Vladimir V. Putin of Russia had “aspired to help” Mr. Trump to win the election and harm Hillary Clinton, a longtime adversary.
By then, both the F.B.I. and the C.I.A. said they had “high confidence” that Russia was trying to help Mr. Trump by hacking into the internal emails of the Democratic National Committee and of some Clinton aides. (The National Security Agency expressed only “moderate confidence” that the Russians were trying to help him.)
Last month, Mr. Comey publicly acknowledged the continuing investigation for the first time at a House hearing on Russia’s influence on the election and said the F.B.I. was examining possible links between Trump associates and Russia for evidence of collusion.
One factor in the C.I.A. analysis last summer was that American intelligence agencies learned that Russia’s cyberattacks had breached Republican targets as well as Democrats. But virtually none of the hacked Republican material came out publicly, while the Russians, working through WikiLeaks and other public outlets, dumped substantial amounts of Democratic material damaging to Mrs. Clinton’s campaign.
Some intelligence officials were wary of pushing too aggressively before the election with questions about possible links between Russia and the Trump campaign because of concerns it might be seen as an improper political attempt to help Mrs. Clinton.
But after her loss, a number of Mrs. Clinton’s supporters have said that Mr. Comey and other government officials should have revealed more to the public during the campaign season about what they knew of Russia’s motivations and possible connections to the Trump campaign.
The classified briefings that the C.I.A. held in August and September for the so-called Gang of Eight — the Republican and Democratic leaders of the House and the Senate and of the intelligence committees in each chamber — show deep concerns about the impact of the election meddling.
In the briefings, the C.I.A. said there was intelligence indicating not only that the Russians were trying to get Mr. Trump elected but that they had gained computer access to multiple state and local election boards in the United States since 2014, officials said.
Although the breached systems were not involved in actual vote-tallying operations, Obama administration officials proposed that the eight senior lawmakers write a letter to state election officials warning them of the possible threat posed by Russian hacking, officials said.
But Senator Mitch McConnell of Kentucky, the Republican majority leader, resisted, questioning the underpinnings of the intelligence, according to officials with knowledge of the discussions. Mr. McConnell ultimately agreed to a softer version of the letter, which did not mention the Russians but warned of unnamed “malefactors” who might seek to disrupt the elections through online intrusion. The letter, dated Sept. 28, was signed by Mr. McConnell, Mr. Reid, Speaker Paul D. Ryan and Representative Nancy Pelosi, the ranking Democrat.
On Sept. 22, two other members of the Gang of Eight — Senator Dianne Feinstein and Representative Adam B. Schiff, both of California and the ranking Democrats on the Senate and House intelligence committees — released their own statement about the Russian interference that did not mention Mr. Trump or his campaign by name.
But they did say that “based on briefings we have received, we have concluded that the Russian intelligence agencies are making a serious and concerted effort to influence the U.S. election.”
“At the least, this effort is intended to sow doubt about the security of our election and may well be intended to influence the outcomes of the election,” they added.
The F.B.I., the N.S.A. and the Office of the Director of National Intelligence also held a classified briefing on Sept. 6 for congressional staff members about the wave of Russian hacks and “the current and ongoing threat facing U.S. political organizations during this national political season,” according to a government official.
These new details show Congress and the intelligence agencies racing in the campaign’s final weeks to understand the scope of the Russian threat. But Democrats and Republicans who were privy to the classified briefings often saw the intelligence through a political prism, sparring over whether it could be construed as showing that the Russians were helping Mr. Trump.
The briefings left Mr. Reid frustrated with the F.B.I.’s handling of Russia’s election intrusion, especially after the agency said in late October — 11 days before the election — that it was re-examining Mrs. Clinton’s emails.
Mr. Reid fired off another letter on Oct. 30, accusing Mr. Comey of a “double standard” in reviving the Clinton investigation while sitting on “explosive information” about possible ties between Russia and Mr. Trump.
“The public,” Mr. Reid wrote said, “has a right to know this information.”