There are some important things the public doesn't know about the so-called "Trump dossier," such as whether the FBI used information from the dossier to win court permission to spy on Americans. But the most important question about the dossier is the simplest: Is it true?

In a seven-hour interview with the House Intelligence Committee Wednesday, FBI Deputy Director Andrew McCabe repeatedly declined to answer whether the bureau has been able to verify the substantive allegations in the dossier, or even to identify a substantive allegation that has been corroborated, according to sources familiar with the questioning.

The dossier portion of the interview began with McCabe being asked if he thought the dossier met the standard of credibility the FBI required to open an investigation. McCabe said he believed it did. He said on more than one occasion that the FBI had worked hard to verify the dossier, telling lawmakers that the FBI had at one point sent investigators to London as part of the effort.

McCabe was asked to point to anything in the dossier that he knew to be true. McCabe noted that the dossier said, accurately, that the unpaid, low-level Trump foreign policy adviser Carter Page visited Moscow in July 2016.

McCabe's questioners were not impressed. Page's Moscow trip was reported in the press at the time it happened; the simple fact that he was in Russia was not a revelation. Lawmakers reminded McCabe that Page's presence in Moscow was long established and then asked again: Was there anything more in the dossier that McCabe now knows to be true? McCabe, according to sources, said he did not know how to answer the question.

The dossier, of course, reported much more than the fact of Page's travel to Moscow. It said Russians linked to Vladimir Putin offered Page money in exchange for persuading Trump to end U.S. sanctions on Russia. Specifically, it said Page met with Igor Sechin, the Putin-connected head of Rosneft, Russia's giant, state-owned oil company, and also with Igor Divyekin, a top official in the Putin government. The dossier reported that Sechin offered to pay Page or other Trump associates tens of millions of dollars to end the sanctions.

None of that has been verified.

On a number of occasions, when asked about what in the dossier had been corroborated by the FBI, McCabe gave answers such as — these are not precise quotes — I can't answer that, or I don't know how to answer that. Indeed, that was McCabe's answer when he was asked for the most important piece of information in the dossier that the FBI had been able to verify.

At one point, McCabe was reminded that another top FBI official had months ago told the House that the bureau had not been able to corroborate the dossier. McCabe's response was noncommittal.

After the questioning established that McCabe would not verify any substantive allegation in the dossier, he was asked if he stood by its veracity. McCabe said he did.

And that was the gist of the questioning on the dossier. McCabe never claimed the FBI had verified the substantive allegations in the dossier, but he also never said the FBI had not been able to verify the dossier's explosive allegations, either.

Just for the record, besides the Page matter, among the stories in the dossier that remain unverified are:

· An alleged 2013 incident in a Moscow hotel involving Trump and prostitutes.

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

· An alleged meeting between close Trump aide Michael Cohen and "Kremlin representatives" in Prague, Czech Republic in August 2016, allegedly attended by a leading pro-Putin Russian legislator.

· An alleged meeting between Viktor Yanukovych, the ousted Ukrainian president, and Putin "in secret on 15 August near Volgograd, Russia" at which Yanukovych confided in Putin that he, Yanukovych, had ordered big kickbacks to be paid to Paul Manafort, who served for a while as Trump campaign chairman.

· An alleged order from Putin to Kremlin staff not to discuss Russian attempts to influence the U.S. election "in public or even in private."

They're all there in the 35-page document. The FBI has been investigating the Trump-Russia matter since summer 2016. Now, the second-highest ranking official in the bureau will not say whether anything in the document, beyond its repetition of information already in the press, has been found to be true.