Richard Gates has emerged as a key figure in special counsel Robert MuellerRobert Swan MuellerSasse: US should applaud choice of Mueller to lead Russia probe MORE‘s investigation of Russia’s interference in the election. 

Mueller on Thursday unveiled new criminal charges against Gates and Paul ManafortPaul John ManafortOvernight Cybersecurity: Lawyer charged in Mueller probe pleads guilty to lying | Sessions launches cyber task force | White House tallies economic impact of cyber crime Lawyer charged in Mueller probe pleads guilty to lying to federal investigators The Hill’s 12:30 Report MORE, his longtime business partner, accusing them of a series of financial crimes including tax evasion, bank fraud and money laundering. 

Observers for weeks had been expecting that Gates, a one-time Trump campaign aide, might strike an agreement with Mueller to avoid going to trial.

The superseding indictment released Thursday deepens the legal peril for Gates.

Seth Waxman, a former federal prosecutor, said the timing of the filing likely aims to maximize the pressure on Gates, in case he is wavering on whether to cooperate with the investigation. 

“It is designed to continue to ratchet up the pressure on Manafort and Gates to flip,” he said.

Waxman said the new filings suggest Mueller is likely sending a clear signal to Gates “that he is not messing around.”

Gates is a key figure for Mueller because of his close relationship with Manafort, President TrumpDonald John TrumpAccuser says Trump should be afraid of the truth Woman behind pro-Trump Facebook page denies being influenced by Russians Shulkin says he has White House approval to root out ‘subversion’ at VA MORE’s former campaign chairman.

Gates and Manafort worked hand-in-hand for more than a decade, including on lobbying work for pro-Russian forces in Ukraine, so his testimony at trial could prove especially damaging for Manafort. 

“If Manafort really did have a second in command comparable to a close confidante, you don’t get much better than that,” said Steven Cash a lawyer at Day Pitney who specializes in criminal litigation and national security-related matters. “It’s like having the second-in-command of a company testify against the CEO.” 

A plea agreement with Gates would put heavy pressure on Manafort to cut a deal of his own. If he flipped, it’s possible he could give Mueller inside information about any contact between the Trump campaign and Moscow during the summer of 2016, a key period when Russia began orchestrating the release of hacked Democratic emails. 

“The Manafort indictment is serious, is ugly and is very likely backed by large volumes of evidence,” said Ron Hosko, a former FBI assistant director. “Gates can drive a final nail.”

President Trump has flatly denied any collusion between his campaign and Russia, describing the allegations as a “hoax.” 

Mueller’s team first unveiled an indictment Manafort and Gates in late October. 

That indictment, which included bank transactions, accused Manafort and Gates of money laundering, bank fraud and other financial crimes stemming from work overseas that predated their involvement in Trump’s presidential campaign.

Both men pleaded not guilty last year.

Former prosecutors say Gates’s testimony, should he choose to cooperate, could help prosecutors sort through their evidence against Manafort. He could also fill in holes in timelines and help walk prosecutors through some of the complex financial transactions that he and Manafort are accused of carrying out.

“In most businesses and white-collar cases, the government really needs a cooperator to explain events,” said Jack Sharman, a former Whitewater special counsel.

The possibility of Gates on the witness stand could be enough to get Manafort to cooperate with Mueller’s prosecutors, which is likely their main goal. 

Manafort worked for Trump’s campaign for six months before resigning under pressure in August 2016 over reports of his dealings with a pro-Russian oligarch in Ukraine. He was in the room for a June 2016 meeting at Trump Tower with a Russian lawyer who had promised Donald Trump Jr.Donald (Don) John TrumpTrump Jr. praises ‘spirit’ of poverty-stricken Indians: ‘Still a smile on a face’ State Dept. says it did not coordinate with Trump Jr. on India speech The Hill’s 12:30 Report MORE damaging information on Hillary ClintonHillary Diane Rodham ClintonWoman behind pro-Trump Facebook page denies being influenced by Russians Trump: CNN, MSNBC ‘got scammed’ into covering Russian-organized rally Pennsylvania Democrats set to win big with new district map MORE’s campaign, and could provide inside information about any contact between the campaign and Russia.

If Gates were to strike a plea deal, he would be the fourth known witness to cooperate with Mueller’s investigation, in addition to former national security adviser Michael Flynn, former Trump campaign adviser George PapadopoulosGeorge Demetrios PapadopoulosGates agrees to testify against Manafort in Mueller probe: report Mueller indictments still miss the mark on Trump-Russia collusion Five key takeaways from the Russian indictments MORE, and a California man ensnared in the probe for selling bank account numbers to foreigners committing identity fraud. 

“I think the question is not, are there going to be more indictments and guilty pleas. I think there will be,” Sharman said. 

“The larger question is ultimately what is the relation of any of those offenses to the original core mission of the special counsel, who was appointed because of concerns over presidential campaign involvement.”