In a secure meeting room under the Capitol last week, lawmakers held in their hands a classified letter written by colleagues in the Senate summing up a secret, new CIA assessment of Russia’s role in the 2016 presidential election.

Sitting before the House Intelligence Committee was a senior FBI counterintelligence official. The question the Republicans and Democrats in attendance wanted answered was whether the bureau concurred with the conclusions the CIA had just shared with senators that Russia “quite clearly” intended to help Republican Donald Trump defeat Democrat Hillary Clinton and clinch the White House.

For the Democrats in the room, the FBI’s response was frustrating – even shocking.

During a similar Senate Intelligence Committee briefing held the previous week, the CIA’s statements, as reflected in the letter the lawmakers now held in their hands, were “direct and bald and unqualified” about Russia’s intentions to help Trump, according to one of the officials who attended the House briefing.

The FBI official’s remarks to the lawmakers on the House Intelligence Committee were, in comparison, “fuzzy” and “ambiguous,” suggesting to those in the room that the bureau and the agency weren’t on the same page, the official said.

The divergent messages from the CIA and the FBI put a spotlight on the difficulty faced by intelligence and law enforcement officials as they try to draw conclusions about the Kremlin’s motives for hacking Democratic Party emails during the 2016 race. Officials are frequently looking at information that is fragmentary. They also face issues assessing the intentions of a country expert at conducting sophisticated “influence” operations that made it hard – if not impossible – to conclusively detect the Kremlin’s elusive fingerprints.

The competing messages, according to officials in attendance, also reflect cultural differences between the FBI and the CIA. The bureau, true to its law enforcement roots, wants facts and tangible evidence to prove something beyond all reasonable doubt. The CIA is more comfortable drawing inferences from behavior.

“The FBI briefers think in terms of criminal standards – can we prove this in court,” one of the officials said. “The CIA briefers weigh the preponderance of intelligence and then make judgment calls to help policymakers make informed decisions. High confidence for them means ‘we’re pretty damn sure.’ It doesn’t mean they can prove it in court.”

The FBI is not sold on the idea that Russia had a particular aim in its meddling. “There’s no question that [the Russians’] efforts went one way, but it’s not clear that they have a specific goal or mix of goals,” said one U.S. official.

The murky nature of the assessments is maddening many lawmakers who are demanding answers about the Kremlin’s role in the presidential race. The FBI, under Director James Comey, is already under fire for dropping a bombshell letter days before the election on the discovery of new emails potentially related to the Clinton private server investigation. The emails proved irrelevant to the case. On Saturday, outgoing Senate Minority Leader Harry Reid, D-Nev., called on Comey to resign, saying the FBI director deliberately kept quiet evidence about Russia’s motives before the election.

With so much of the evidence about Russia’s alleged role in the election shrouded in secrecy because of strict classification rules, Democrats and Republicans in Washington who have access to the underlying intelligence say they have struggled to make their respective cases, leaving an already deeply divided public convinced that both sides are shading their conclusions to help the candidate they backed on Election Day.

The clamor from Democrats and some Republicans for a more fulsome accounting prompted the White House on Friday to announce that President Barack Obama had ordered a full review of Russian cyber actions during the 2016 campaign. The president wants the report to be completed before he leaves office next month. Officials said Obama intends to declassify as much of the report as possible. Lawmakers, in turn, want the review to be accompanied by a joint congressional investigation.

“Only in this way can the American people know the extent of Russian interference and we can attempt to inoculate ourselves against continued meddling in our elections,” said Rep. Adam Schiff (California), the ranking Democrat on the House intelligence panel, who has been briefed but did not comment on the information he has learned.

Sen. Angus King, I-Maine, a member of the Senate Intelligence Committee, said the intelligence community’s information needs to be made public “not to revisit this election, but to see that this doesn’t happen again.” Russia regularly tries to influence European politics and elections, “and I don’t want this to be the case here,” he said.

King said he does not believe Moscow’s efforts end with Trump’s election. “It could happen in the midterms. It could be in the next presidential election. They have shown us that they are capable and willing to do it here. For us not to react with the highest level of investigation and preparing responsive measures would be negligent,” he said.

Meanwhile, top Republicans on the committee have pointed to the possible ambiguity of the evidence to question the soundness of the claim that Russia acted to help Trump. “There is no clear evidence – even now,” said Rep. Devin Nunes, R-Calif., the panel’s chairman. “There’s a lot of innuendo, lots of circumstantial evidence, that’s it.”

At the start of the House Intelligence Committee briefing, the senior FBI official walked lawmakers through the evidence that the bureau thought was credible about Russia’s role in the election, according to officials in attendance.

It didn’t take long for the conversation to turn to the statements that the CIA briefer had made to the Senate panel, making the case for the first time that Russia intended to help Trump win the election.

Previous CIA assessments said Moscow’s goal were more cautious, limited to undermining faith in the U.S. electoral system. In earlier statements to the intelligence committees in Congress, the agency stopped short of saying the intrusions were meant to benefit one candidate over another.

During the nearly two-hour briefing, the Democratic lawmakers in the room, again and again, tried to pin the FBI official down on whether the bureau believed that Russia had a preference in who won the election.

“It was shocking to hold these [CIA] statements made about Russian intentions and activities, and to hear this guy basically saying nothing with certainty and allowing that all was possible,” said an official who attended the briefing. The official spoke on the condition of anonymity to describe sensitive discussions.

Many of the Republican lawmakers welcomed the FBI’s caution. They didn’t think the CIA had a basis for coming to the conclusions presented to the Senate panel. Some of the Republicans on the House side thought it would have been more logical for the CIA to conclude that Russia preferred Clinton because she was a known commodity and because Trump talked during the campaign of expanding the U.S. military, something Russia might interpret as a threat, according to officials.

At one point during the discussion in the secure room, a Republican lawmaker turned to his Democratic colleagues and said the back-and-forth suggested that “Republicans are from Mars, Democrats are from Venus,” according to an aide who was present, adding: “We’re looking at the same evidence and drawing very different conclusions.”

(c) 2016, The Washington Post · Ellen Nakashima, Adam Entous