Compromising and unproven allegations that U.S. president-elect Donald Trump is vulnerable to blackmail by the Russian government will be his burden to disprove. But whether true or not, the claims may have already wrought damage.

A CNN report on Tuesday about a two-page synopsis appended to classified intelligence documents includes claims that Russian operatives have compromising personal and financial material on him that could harm his presidency.

A 35-page dossier citing an unnamed former British intelligence source was posted in full by BuzzFeed. There are claims made in that dossier that were presented as part of a briefing last week to Trump and President Barack Obama.

None of the allegations have been substantiated. News outlets including the New York Times and Washington Post acknowledged they had the information for months, but refrained from publishing stories because much of it was unverifiable.

In the so-called "post-truth" political era, though, it may still bring trouble for Trump as he works to allay concerns that America's incoming president might be submitting to pressure by a foreign power.

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Trump speaks to Pence during the news conference Wednesday. (Evan Vucci/Associated Press)

With a recent Quinnipiac University survey showing Trump has only a 37 per cent approval rating, the onus will be on him to debunk the reports through an investigation into what the Russians may or may not have on him.

"If he's confident that there's nothing out there, he probably should launch a thorough investigation so he can be confident that the findings will clear him," says Geoffrey Skelley, a nonpartisan analyst and editor of the Sabato's Crystal Ball political newsletter.

"In a black-and-white world, it would be reassuring to the public that there isn't anything that could threaten the nation via some kind of blackmailing of the president."

While Skelley believes a serious investigation into the assertions would be in Trump's best interests, he notes that the blackmail storyline gives some political opponents suspicious about his "hesitancy to criticize Russia" a possible explanation.

"It feeds exactly into that narrative," he says.

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Russian President Vladimir Putin attends an Orthodox Christmas service at St. George monastery outside Novgorod, Russia on Jan. 7. Trump said Wednesday his relationship with Putin is an improvement over America's current 'horrible relationship with Russia.' (Sputnik/Mikhail Klimentyev/Kremlin via Reuters)

The reports could also expose Trump's deepening feud with intelligence agencies. That relationship became fraught after Trump's initial refusal to believe an intel report laying out a case for why Russians likely hacked into the U.S. electoral system to try to tilt the election outcome in his favour.

At his first press conference in nearly 170 days on Wednesday, Trump's denial about the veracity of the memos published by BuzzFeed took a remarkable detour, resulting in an accusation directed at his own security establishment.

Calling the report "nonsense," Trump told reporters the leak was "released by maybe the intelligence agencies, who knows? But maybe the intelligence agencies, which would be a tremendous blot on their record if they, in fact, did that."

A 'very odd' display

It was a "very odd" display of apparent distrust in the intel community, says Robert Jervis, a Columbia University professor specializing in national security policy and intelligence.

"As usual, it's hard to understand the syntax, but he seemed to be implying, 'The intelligence community is really out to get me.'"

It may not be the best way to establish a precedent of trust in a security establishment, Jervis says, though he notes that U.S. intelligence agents are known for being thick-skinned.

Although Trump later acknowledged that "as far as hacking" into the U.S. electoral system, "I think it was Russian," those kinds of hot-then-cold appraisals about the credibility of the Central Intelligence Agency's efforts could drive away officers.

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Former CIA director Michael Morell says he was surprised that unverified documents would be shown to the president-elect. (Reuters)

Former CIA chief Michael Morell warned in a New York Times op-ed last week: "If the president rejects out of hand the CIA's work, or introduces uncertainty by praising it one day only to lambaste it on Twitter that afternoon, many officers will vote with their feet."

That isn't to say the dossier should be believed, however. Morell acknowledged in a CNN interview he was surprised that unverified documents would be shown to the president-elect, adding that he read in the memos "small bits of information that I knew were true" as well as material "that was absolutely not true."

Until Tuesday, the press had largely held off on reporting about the leaked memos as the allegations circulated around Capitol Hill because the claims could not be corroborated. Republican Senator John McCain said the information was also brought to his attention, but he passed it along to the FBI.

Anonymous source

The intel came from one anonymous source, a former British agent for MI6 hired by Trump's political opponents.

Multiple reports, including by the BBC and the Wall Street Journal, have identified the former MI6 operative Christopher Steele.

According to CNN, the FBI and other U.S. intelligence agencies are looking into the authenticity of the dossier's conclusions, which also allege that Trump surrogates and Russian go-betweens working on behalf of the Kremlin shared information during the election campaign.

The main source of the memos, according to reports, is considered "credible." And, as national security expert Elizabeth Goitein notes, "This country kills people based on sources from intelligence we deem credible."

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White House press secretary Josh Earnest speaks during the daily briefing at the White House on Wednesday. Earnest answered questions about Trump and intelligence briefings. (Susan Walsh/Associated Press)

More important is that the FBI is investigating Trump surrogates' ties to Russia, says Goitein, who co-directs the Brennan Center for Justice's Liberty and National Security Program.

While an FBI investigation is not itself proof of wrongdoing, the bureau also sought and reportedly obtained a warrant from the Foreign Intelligence Surveillance Court. Such warrants are available "only if the FBI has probable cause to believe that the target is an agent of a foreign power," Goitein says.

News of the warrant, compounded with the fact Trump was about to hold his first press conference in nearly six months, may help explain why the reports finally came out now.

"It sounds like the press just reached a tipping point," says Skelley, the political analyst.

"Official agencies were making serious inquiries related to this, and it's just been out there. It seemed a matter of time."