FBI and Justice Department officials have told congressional investigators in recent days that they have not been able to verify or corroborate the substantive allegations of collusion between Russia and the Trump campaign outlined in the Trump dossier.

The FBI received the first installment of the dossier in July 2016. It received later installments as they were written at the height of the presidential campaign, which means the bureau has had more than a year to investigate the allegations in the document. The dossier was financed by the Hillary Clinton campaign and compiled by former British spy Christopher Steele.

An August 24, 2017 subpoena from the House Intelligence Committee to the FBI and Justice Department asked for information on the bureau's efforts to validate the dossier. Specifically, the subpoena demanded "any documents, if they exist, that memorialize DOJ and/or FBI efforts to corroborate, validate, or evaluate information provided by Mr. Steele and/or sub-sources and/or contained in the 'Trump Dossier.'"

According to sources familiar with the matter, neither the FBI nor the Justice Department has provided documents in response to that part of the committee's subpoena. But in face-to-face briefings with congressional staff, according to those sources, FBI and DOJ officials have said they cannot verify the dossier's charges of a conspiracy between the Russian government and the Trump campaign.

The news appears to contradict recent statements from some top Democrats. "A lot of it has turned out to be true," Rep. Adam Schiff, ranking Democrat on the House Intelligence panel, told the Wall Street Journal on Wednesday.

"The biggest thing that I think people need to realize about the dossier is that Christopher Steele discovered that the Russians were embarked on a broad effort to help the Trump campaign before our own intelligence agencies came to the same conclusion," Schiff told the Journal. "In the broadest outline of what he investigated, he proved more than prescience — he proved accurate in terms of the Russian involvement and what their motivations were."

There have been many questions surrounding the dossier. Who paid for it? Who were its sources? Did the FBI use it as a basis to request a secret court's authorization to spy on Americans? But the most important question about the dossier is the most basic one: Is it true?

The dossier, 35 pages long, contains many specific assertions that could be verified by an organization with the resources of the FBI -- verified, that is, if they were accurate in the first place. Here are a few:

• The alleged 2013 Moscow hotel episode, in which "TRUMP's (perverted) conduct in Moscow included hiring the presidential suite of the Ritz Carlton hotel, where he knew President and Mrs. OBAMA (whom he hated) had stayed on one of their official trips to Russia, and defiling the bed where they had slept by employing a number of prostitutes to perform a 'golden showers' (urination) show in front of him. The hotel was known to be under FSB control with microphones and concealed cameras in all the main rooms to record anything they wanted to."

• Trump's alleged participation in other "sex parties" in St. Petersburg.

• Alleged meetings between Carter Page, the low-influence, short-term Trump foreign policy advisor, and Igor Sechin, head of Rosneft, Russia's giant state-owned oil company, as well as between Page and Igor Divyekin, a top official in the Putin government, during Page's trip to Moscow in July 2016.

• An alleged offer from Sechin to give Page and/or Trump associates "the brokerage of up to a 19 percent (privatised) stake in Rosneft" -- worth potentially billions of dollars -- in return for ending U.S. sanctions against Russia.

• An alleged meeting between close Trump aide Michael Cohen and "Kremlin representatives" in Prague, Czech Republic in August 2016. The dossier reported that Cohen also met "clandestinely in an EU country" with lawyers from the Putin government, also in August 2016, "to clean up the mess left behind by western media revelations of TRUMP ex-campaign manager MANAFORT's corrupt relationship with the former pro-Russian YANUKOVYCH regime in Ukraine and TRUMP foreign policy advisor, Carter PAGE's secret meetings in Moscow with senior regime figures in July 2016."

• The alleged attendance at the alleged Cohen meeting of a leading pro-Putin legislator, Konstantin Kosachev, "an important figure in the TRUMP campaign-Kremlin liaison operation" who "facilitated the contact in Prague and by implication, may have attended the meeting/s with COHEN there in August."

• An alleged meeting between Viktor Yanukovych, the ousted Ukrainian president, and Putin "in secret on 15 August near Volgograd, Russia" -- a meeting at which "the western media revelations about MANAFORT and Ukraine featured prominently on the agenda." The dossier reported that "YANUKOVYCH had confided in PUTIN that he did authorise and order substantial kick-back payments to MANAFORT as alleged but sought to reassure him that there was no documentary trail left behind which could provide clear evidence of this."

• An alleged directive from Putin in which Putin "issued direct orders" to Kremlin staff not to discuss Russian attempts to influence the U.S. election "in public or even in private."

Some Republicans point out that at least one group of assertions, the ones concerning Michael Cohen, have been convincingly debunked. (Cohen has produced proof that he was not in the Czech Republic, or even in Europe, when the purported meeting took place.) The dossier attributed the Cohen story to a "Kremlin insider" who was "speaking in confidence to a longstanding compatriot friend." Investigators want to know if that insider-compatriot line of sourcing provided other, equally unreliable information in the dossier.

Whatever the case, the bottom line appears to be that the FBI and the Justice Department are not vouching for the accuracy of the substantive allegations of collusion in the dossier. Indeed, a careful reading of Schiff's interview with the Wall Street Journal suggests even the combative top Democrat on the House Intelligence Committee isn't doing so, either.

The most important thing about the dossier, Schiff said, is that Steele discovered the Russian "broad effort" to influence the election before U.S. intelligence agencies did. Steele was accurate "in the broadest outline of what he did," Schiff claimed, which was reporting "Russian involvement" and "what [Russian] motivations were."

That's fine, as far as it goes -- after all, investigators unanimously agree that Russia tried to influence the election -- but what about the Trump campaign? What about all those specific allegations of coordination between Team Trump and the Russians? Those were the most explosive parts of the dossier. And they remain unverified.