Manafort, who was Donald Trump’s campaign manager for part of 2016, is currently under house arrest while facing trial for 23 counts including money laundering, conspiracy and making false statements. In the past, Mueller, the special counsel in the Russia investigation, has claimed that Manafort is a flight risk because of his international connections. A judge has set bail at $10 million, a daunting sum that Manafort has been struggling to meet.

On Monday night, Mueller filed a motion to deny Manafort bail because the former campaign manager allegedly tried in February to tamper with witnesses in his case by talking to them and texting them. The underlying issue is money that Manafort allegedly paid to a group of European politicians called “the Hapsburg group.” That money was allegedly lobbying funds used on behalf of pro-Russian Ukrainian political interests.

Manafort allegedly tried to contact witnesses in the case to coach them to say that the money to the Hapsburg group had been paid in Europe, not America. Part of the governments case is that the Hapsburg group took place in the United States. One message from Mueller to a witness read, “We should talk. I have made clear that they worked in Europe.” The motion describes one witness as Person D1 and says, “Person D1 has told the government that he understood Manafort’s outreach to be an effort to ‘suborn perjury,’ because Person D1 knew that the Hapsburg group worked in the United States—not just Europe.”

This move increases the pressure on Manafort. The open question is whether the latest turn of the screw will force him to make a plea bargain and possibly flip on his previous employer, the president of the United States.