Amid a flurry of new developments in special counsel Robert Mueller’s investigation, there’s one revelation that’s particularly dramatic.

That is: A low-level Trump adviser was told as early as April 2016 that the Russians had “dirt” on Hillary Clinton, in the form of “thousands of emails.”

It’s a potentially crucial new piece of information that raises even more questions about just what, exactly, the Trump campaign knew about the Russian effort to hack and release leading Democrats’ emails — and whether they had collaborated with or advised that effort in any way.

The Trump adviser in question is George Papadopoulos — a foreign policy adviser to the campaign who, it was revealed in a document unsealed Monday, had been arrested back in July for making false statements to the FBI, and now appears to have made a deal to cooperate with Mueller’s probe into Russian interference.

Papadopoulos now admits to various contacts with Russians during his tenure as a Trump adviser in 2016, but the most eyebrow-raising revelation relates to a conversation he had with someone, identified as “the Professor” in the charging document, who he knew had connections to the Russian government. This professor (identified as Joseph Mifsud by the Washington Post) told Papadopoulos that the Russians had “dirt” on Clinton, that “the Russians had emails of Clinton,” and that “they have thousands of emails.”

This charging document then goes on to describe, at length, Papadopoulos’s contacts with other campaign officials as he labored unsuccessfully to try to set up a trip to Russia for the candidate.

But aside from this mention, the document remains conspicuously silent about the obvious question of whether Papadopoulos told other Trump campaign advisers what he had heard about that Clinton email “dirt.”

That’s an enormously important question — and the answer to it could be crucial to the investigation.

Could it all, in the end, come back to emails?

Questions about Trump, Russia, and the 2016 campaign are often framed in terms of whether there was “collusion.” But in addition to not actually being a legal term, collusion is also a rather vague term.

Some people, for instance, argued that the meeting between Donald Trump Jr., Manafort, and a Russian lawyer in July was proof of collusion. After all, the lawyer was said to be working with the Russian government, and to have negative information on Hillary Clinton. And they did have that meeting, so, some say, isn’t that collusion?

But so far, it hasn’t been shown that that meeting actually resulted in anything significant. All parties involved are claiming that it was brief and uneventful — one of many quick things in a rapid-fire campaign — and so far, no one has come up with any information to prove differently.

For this scandal to truly shake up the political status quo and put the Trump presidency at risk, there would have to be evidence of something much more damning and concrete.

And it’s always seemed that one possibility for that damning and concrete thing would be the email hacks.

The Russia-linked hacks and leaking of prominent Democrats’ emails, most notably the Democratic National Committee (whose emails were leaked online in July 2016) and Clinton campaign chair John Podesta (whose emails were posted by WikiLeaks in the final weeks of the election), is something that was not only scandalous but also illegal.

And if the Trump campaign or Trump associates did know of or were involved in those hackings and leaks in any way — something they’ve denied — it would elevate this scandal to an entirely new level.

Whom did Papadopoulos tell about this Russian “dirt” on Clinton?

Now comes the news that Papadopoulos heard as far back as April 2016, from a source with connections to the Russian government, that the Russians had “dirt” on Hillary Clinton in the form of “thousands of emails.”

Overall, the charging document portrays Papadopoulos as determined to ingratiate himself with the Trump campaign, bragging repeatedly about his contacts with Russians. So it certainly seems implausible that he’d keep this potentially important news — that the Russians had thousands of Clinton-related emails! — to himself.

And that presents the possibility that top Trump advisers were informed about the matter long before the email leaks started spilling out in the summer of 2016.

For now, this is only a possibility. It is also possible that Papadopoulos said nothing, or that his attempts to tell Trump advisers about this were ignored. It is also possible that the information was passed on, but in a vague or nonspecific form, and no follow-up ensued. (After all, some in the Trump campaign seem to have been under the impression that the emails the Russians had were Clinton’s deleted personal emails, which does not seem to have been the case.)

However, a tip-off to the Trump campaign would certainly shed more light on why Trump oddly called on Russia to release Clinton’s emails during a July 27, 2016, press conference. “Russia, if you’re listening, I hope you’re able to find the 30,000 [Hillary Clinton] emails that are missing,” he said. “I think you will probably be rewarded mightily by our press. Let's see if that happens. That will be next.” (Curiously, he then didn’t hold another press conference for the rest of the campaign.)

Furthermore, Mueller has managed to keep this Papadopoulos news under wraps for some time — the arrest was back in July and only made public on Monday, after Manafort and Gates were indicted. And Papadopoulos appears to have made a plea deal including some cooperation. Much could hinge on what he says.