Paul Manafort's indictment was big. Trump 'volunteer' George Papadopoulos's plea may be even bigger

Former Trump campaign manager Paul Manafort has been indicted; his long-time deputy Rick Gates also faces charges. And George Papadopoulos, a 30-year-old junior campaign "volunteer" who recently listed the Model United Nations among his foreign-policy credentials, is the first conviction secured by Special Counsel Robert Mueller's team.

If you think you know who among these three ex-Trump campaign officials might be the biggest catch, though, think again.

The trio includes two top officials, but legal scholars believe the small-time player among them in Mueller's probe into Russian election interference could be the most significant.

Manafort, Gates and Papadopoulos could be "flipped" under pressure of prospective jail time to strike deals and help bring forth more charges.

The aim by prosecutors, experts say, would be to implicate higher-level associates of U.S. President Donald Trump.

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Manafort and Gates surrendered to the FBI on Monday morning on 12 counts, primarily for financial crimes such as money laundering as well as so-called "Section 1001 violations" involving misleading federal authorities. Both have pleaded not guilty to all charges.

But tantalizing as it may be for those rooting for Mueller's team to imagine what those developments meanfor the ongoing probe, it's the more obscure defendant, Papadopoulos, who experts believe is the biggest get.

In a development on Monday, newly unsealed court records revealed that Papadopoulos, a low-level campaign aide and former energy adviser before he joined the Trump campaign, pleaded guilty on Oct. 5 to lying to FBI investigators. He faces up to six months in jail and a fine of up to $9,500.

That means Mueller's team already has had, possibly for weeks, a co-operating witness, albeit one dismissed by the White House on Monday as merely a "volunteer" with "extremely limited" experience.

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"It could be that the Papadopolous plea may be the most significant thing of all, long-term," said legal scholar Mark Osler, a former federal prosecutor.

There's a compelling reason why.

'This is a very strong punch in your face for Manafort and Gates.'- Former federal prosecutor John Flannery

"He's apparently now telling the truth, and that could be a bad thing for some people within the Trump administration," Osler says.

While Manafort and Gates are accused of serious financial crimes, their indictment never mentions the Trump campaign directly. Not so when it comes to Papadopoulous. He pleaded guilty to lying to the FBI about an April 2016 discussion he had with a professor tied to the Kremlin regarding "dirt" about Trump's political rival Hillary Clinton."

"The Manafort-Gates indictment stands alone. It's in a silo," Osler says. "Do they want him to flip? Sure, they do, but even if Manafort doesn't flip, if Gates does, it could be almost as significant because of what he knows."

After Manafort was ousted from the Trump campaign in August 2016, Gates outlasted him for another eight months, resigning this April.

Legal scholars describe the Papadopoulous plea as a "pocket indictment" viewed as a reliable, back-pocket chip to play whenever prosecutorssee fit.

Start at the bottom withminor player

Prosecutors tend to start at the bottom and work their way to the top, says Stefan Cassella, a former federal prosecutor and financial crimes expert who has studied the 31-page indictment.

"You flip a minor player to testify against a major player," he said. "You don't charge someone with a [Section] 1001 violation like this and keep it sealed unless he's co-operating, so we'll see against whom he co-operates."

Cassella said the Manafort and Gates indictment "could be characterized as having nothing to do with the Russians" or that Mueller's investigation is only bearing fruit when he oversteps his mandate. (The president himself argued that the charges against Manafort seemed to involve a timeline that predated his presidential campaign's start in summer 2015: "Sorry, but this is years ago, before Paul Manafort was part of the Trump campaign," Trump wrote.)

Which is why the unusual move to unseal the Papadopoulous records revealing the Russia connection at the same time as the Manafort announcement is so savvy, Cassella says.

"It completely rebuts them on that argument," he said. "Well played."

Chicago law professor and former federal prosecutor Andrew Boutros didn't anticipate the Papadopoulos development, but he predicted Manafort's indictment as well as some of the charges he's facing related to his being an unregistered foreign agent.

That the special counsel is showing he's moving forward in the investigation and getting results matters in terms of optics, Boutros said.

'They now have something'

"It validates his mandate. So he now has something to show for the expenditure of significant funds, an incredibly expensive investment of resources. They now have something."

Boutros said as he understands it, the charges have nothing to do with the campaign, but what is interesting is that Manafortonce held such a high-level position as campaignmanager.

In that sense, former federal prosecutor John Flannery said the serious financial charges brought against Manafort might seem "vanilla."

The timing of Monday's developments is also key. The Manafort indictment before the end of the month is likely tied to a five-year statute of limitations on tax-related charges. "Plainly, the hope is to pressure Manafort to co-operate against others," Flannery said.

"This is a very strong punch in your face for Manafort and Gates, and it's a significant first step for an investigator to choose a high-valued target and to publicly put pressure on him to flip."

And if Manafort could be caught up in a probe for a violation of the misleading statements under the Foreign Agents Registration Act, it stands to reason that former national security adviser Michael Flynn might be vulnerable to being indicted next, Flannery said.

Flynn, like Manafort, retroactively registered as a foreign agent. Flynn'sconsulting firm also accepted $530,000to represent Turkey's interests while he served in the campaign. And he may have misled FBI agents by reportedly denying to themthat he ever discussed sanctions with Russian ambassador Sergey Kislyak.

If investigators have found enough to charge him, lawyers say, one possibility is that Flynn is already co-operating with Mueller's team.

One way or another, he's seen as a likely target for future indictments, Flannery said.

"I think Mueller is telling Trump, by his actions, we just banged your campaign manager. And we're coming for you with you or without the others."