The Obama administration is under intense pressure to release evidence confirming Russian interference in the presidential election before leaving office.

The administration up until now has provided little documentation to back up its official October assessment that the Russian government was attempting to interfere in the U.S. election.

Nor has it corroborated subsequent leaks from anonymous officials contending that the CIA believes the campaign was an attempt by Russian President Vladimir Putin to ensure Donald Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE’s victory.

President Obama has ordered the intelligence community to produce a complete review of its findings before Trump takes office on Jan. 20. The White House has said it will make as much of the report public as it can.

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But officials have warned that the document will contain “highly sensitive and classified information” and it is unclear how much concrete evidence it will be able to release.

Releasing any documentation of Russian interference would be a slap in the face to Trump, who has rejected assertions that the Kremlin was involved in the hacks on the Democratic National Committee (DNC) and Hillary Clinton Hillary Diane Rodham ClintonDemocratic groups using Bloomberg money to launch M in Spanish language ads in Florida The Hill's Campaign Report: Presidential polls tighten weeks out from Election Day More than 50 Latino faith leaders endorse Biden MORE campaign chairman John Podesta.

The president-elect and his team have treated any suggestion of Russian involvement as an attack on the legitimacy of his election, and Republican leaders in Congress have treaded carefully on the issue.

The firestorm ignited by the CIA’s assessment has spurred calls from both parties for the administration to provide proof of Russian meddling.

In late November, seven Democrats on the Senate Intelligence Committee urged the White House to declassify “additional information concerning the Russian Government and the U.S. election.”

As of last week, they had not yet received a response.

The House Intelligence Committee earlier this month demanded a briefing on the subject but was rebuffed by intelligence leaders, who said they will not brief Congress again until the completion of the report for the White House.

Journalists have also pushed for more documentation.

Vice journalist Jason Leopold and Ryan Shapiro, a Ph.D. candidate at the Massachusetts Institute of Technology (MIT), filed a Freedom of Information Act (FOIA) lawsuit against the CIA, the FBI, the Department of Homeland Security and the office of the director of national intelligence seeking records pertaining to Russian interference.

And even Trump’s transition team has said the White House should provide definitive proof to back up its claims.

"If the CIA Director [John] Brennan and others at the top are serious about turning over evidence … they should do that," Trump aide Kellyanne Conway said earlier this month. "They should not be leaking to the media. If there's evidence, let's see it."

Obama has asked the public to take the assessment of Russian interference largely on faith, suggesting that the American people already know everything they need to know to accept the conclusions of the CIA report.

"There are still a whole range of assessments taking place among the [intelligence] agencies," Obama told NPR earlier this month, referring to the report. “But that does not in any way, I think, detract from the basic point that everyone during the election perceived accurately — that in fact what the Russian hack had done was create more problems for the Clinton campaign than it had for the Trump campaign.”

Julian Assange, the founder of WikiLeaks, which published the stolen emails, has denied that the Russian government gave them the files.

Private security firms have provided more detailed forensic analysis linking two well-known Russian intelligence groups to the data breach at the DNC.

Beyond that, the evidence of Russian interference is compelling, though circumstantial.

Russia has a long history of trying to influence elections across Europe, and intelligence experts say it’s plausible that Putin would see an upside to a Trump White House, given his expressed desire to “get along” with the Kremlin.

He hinted in the fall that he might refuse help to some NATO allies should they be attacked by Russia. The statement sent shock waves through the foreign policy community, as the alliance’s chief purpose has long been to serve as a check on Russian aggression.

Although there is disagreement among lawmakers about whether Russia intended to help Trump, few disagree that the DNC and Podesta hacks were in some way an attempt to meddle in the election. Public reporting and previous briefings by intelligence agencies appear to have convinced them of that.

“There are 100 United States senators. ... I would say that 99 percent of us believe that the Russians did this, and we’re going to do something about it,” Sen. Lindsey Graham Lindsey Olin GrahamSenate GOP aims to confirm Trump court pick by Oct. 29: report The Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting Senate GOP sees early Supreme Court vote as political booster shot MORE (R-S.C.) told CNN’s Jim Sciutto on “The Situation Room” on Tuesday.

Lawmakers have vowed to hold hearings on the matter when Congress returns in January.

Obama, meanwhile, has promised to deliver his report to Congress and release what he can as soon as the intelligence community completes it.

“I’m sure what is happening right now is they are going through the calculus of, ‘How much intelligence, how many sources and methods are we willing to burn to make our point?’” said one former White House official.

“My guess is they will have information that indicates course of conduct and links to activities that suggest motivation,” but no smoking gun that will convince those who aren’t already convinced, he said.

The president has not shied from breaking with Trump during his final days in office.

Obama last week undid a regulatory framework seen as key to any implementation of Trump’s proposed Muslim registry.

The administration also declined last week to veto a United Nations resolution condemning Israeli settlements, a move denounced by Trump and the Israeli government.

“There is one president at a time. President Obama is the president of the United States until Jan. 20 and we are taking this action, of course, as U.S. policy,” deputy national security advisor Ben Rhodes said of the U.N. vote.

Some details of the CIA’s assessment may become public before the completion of the review.

The administration is reportedly preparing to issue a slate of retaliatory measures against Russia, including sanctions. To levy sanctions, the White House will have to offer some proof — although the standard is softer than “beyond a reasonable doubt.”

“I think the link between what [the public] gets to see and whatever retaliatory action [Obama takes] is going to be very, very tight,” the former official said.

“Showing information is a necessary precondition for most of the public types of retaliation that have been contemplated.”

--Updated at 11:18 a.m.