– The first criminal charges filed in the investigation of President Donald Trump's campaign aides and Russia's meddling in the 2016 election come straight from a well-thumbed playbook of white-collar crime prosecutions — reward defendants who cooperate, drop the hammer on those who won't, and scare others into talking.

The harsh indictments of Trump's former campaign manager and his deputy — and news that a third former campaign aide has been secretly cooperating with investigators since July — are a clear sign that special counsel Robert Mueller has adopted a bare-knuckle strategy and that more indictments are almost certain, according to former prosecutors.

"I think this sends a message to people in the cross hairs that this is serious, and they should govern themselves accordingly," said Robert Capers, the former top federal prosecutor in the Eastern District of New York, a traditional clearinghouse for organized-crime prosecutions and complex terrorism cases.

Peter Zeidenberg, a former public corruption prosecutor at the Justice Department, said he thought more charges were coming soon. "They've got all kinds of irons in the fire, I am quite sure," he said.

Mueller, a former FBI director and federal prosecutor, has led the investigation since May to determine whether anyone in the Trump campaign actively cooperated with a Russian intelligence scheme to undermine U.S. democracy and damage Hillary Clinton's chances last fall. But Mueller also has the authority to prosecute other crimes he finds.

Paul Manafort, a wealthy Washington lobbyist and power broker who ran the Trump campaign for several critical months last year, and his top business and political aide, Rick Gates, were the first to take the hit.

They were arraigned Monday in federal court on a dozen charges of fraud, conspiracy and money laundering in an alleged scheme to conceal more than $75 million overseas without paying taxes, and using millions to buy luxury cars, expensive suits and fancy homes. Both pleaded not guilty.

But just as the White House was celebrating that the arrests were not linked to Russian meddling, Mueller's team dropped a bombshell: A 30-year-old foreign policy adviser, George Papadopoulos, had already pleaded guilty to lying about his contacts with Russians offering "dirt" on Clinton — and had been secretly assisting prosecutors for months.

Papadopoulos cut a plea deal that means he will probably serve no more than six months in prison. In court papers, he was described as a "proactive" cooperator, a term that veteran prosecutors said sometimes signals that a defendant has been wearing a hidden recording device to gather evidence on others.

"The signal [Mueller] sends to every other potential witness is pretty clear," said Randall Eliason, a former federal prosecutor in Washington and a law professor at George Washington University. "Be like George, come in and cooperate, and cut a deal. If you stonewall us, you'll end up like Manafort."

Manafort and, to lesser extent, Gates, risk significant prison sentences if they are convicted and do not assist Mueller's investigation, perhaps by implicating others, according to a former senior Justice Department prosecutor who asked not to be identified discussing an active case.

"We'll see how strong they are when they're facing prison," he said.

In a court filing Tuesday, Mueller's office argued that Manafort poses a significant flight risk, noting that he keeps three U.S. passports with different identification numbers and submitted 10 passport applications in as many years.

Manafort and Gates are on home confinement pending a hearing Thursday to set bail terms. Manafort pledged to pay a $10 million penalty and Gates a $5 million one if they failed to appear.

Lawyers and others familiar with the investigation said Mueller's dramatic one-two roundhouse punches should instill dread among individuals and professional services companies who might be implicated by Manafort, Gates, Papadopoulos or others caught up in the investigation.

Like Manafort, some of those at risk, they said, are part of Washington's distinct business culture — derided by Trump as denizens of "the swamp" — high-priced companies that specialize in legal representation, lobbying and public relations in the political sphere.

The investigation already has spread across party lines. Democratic super-lobbyist Tony Podesta stepped down from his lobbying business Monday. His company, the Podesta Group, had worked with Manafort to represent a pro-Kremlin faction in Ukraine.

And Sam Clovis, a former Trump campaign co-chairman and radio host who sent e-mails to Papadopoulos encouraging his efforts to set up meetings with Russian officials during the campaign, has hired a lawyer and, according to NBC News, appeared before the grand jury Mueller is using.

Clovis' lawyer, Victoria Toensing, said Clovis "vigorously opposed" any trips to Russia by Trump or his staff and, as "a polite gentleman from Iowa," was only trying to be courteous to Papadopoulos. She said in a statement that Clovis, who has been nominated for a senior job in the Department of Agriculture, hasn't communicated with Papadopoulous since the election.

The Washington Post contributed to this report.