American allies, including the British and the Dutch, had provided information describing meetings in European cities between Russian officials — and others close to Russia's president, Vladimir V. Putin — and associates of President-elect Trump, according to three former American officials who requested anonymity in discussing classified intelligence.

Separately, American intelligence agencies had intercepted communications of Russian officials, some of them within the Kremlin, discussing contacts with Trump associates.

As Inauguration Day approached, Obama White House officials grew convinced that the intelligence was damning and that they needed to ensure that as many people as possible inside government could see it, even if people without security clearances could not. Some officials began asking specific questions at intelligence briefings, knowing the answers would be archived and could be easily unearthed by investigators — including the Senate Intelligence Committee, which in early January announced an inquiry into Russian efforts to influence the election.

At intelligence agencies, there was a push to process as much raw intelligence as possible into analyses, and to keep the reports at a relatively low classification level to ensure as wide a readership as possible across the government — and, in some cases, among European allies. This allowed the upload of as much intelligence as possible to Intellipedia, a secret wiki used by American analysts to share information.

There was also an effort to pass reports and other sensitive materials to Congress. In one instance, the State Department sent a cache of documents marked "secret" to Senator Benjamin Cardin of Maryland days before the Jan. 20 inauguration. The documents, detailing Russian efforts to intervene in elections worldwide, were sent in response to a request from Mr. Cardin, the top Democrat on the Foreign Relations Committee, and were shared with Republicans on the panel.

More than a half-dozen current and former officials described various aspects of the effort to preserve and distribute the intelligence, and some said they were speaking to draw attention to the material and ensure proper investigation by Congress. All spoke on the condition of anonymity because they were discussing classified information, nearly all of which remains secret, making an independent public assessment of the competing Obama and Trump administration claims impossible.

Sarah Isgur Flores, Mr. Sessions's spokeswoman, said "there was absolutely nothing misleading about his answer" because he did not communicate with the ambassador in his capacity as a Trump campaign surrogate. She said Mr. Sessions had at least 25 conversations in 2016 with ambassadors from a range of nations — including Britain, Japan, China, Germany and Russia — while on the Senate Armed Services Committee.