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Editor’s Note: Paul Callan is a CNN legal analyst, a former New York homicide prosecutor and current counsel at the New York law firm of Edelman & Edelman PC, focusing on wrongful conviction and civil rights cases. Follow him on Twitter @paulcallan. The opinions expressed in this commentary are his own.

(CNN) —  

Paul Manafort could be in big trouble. The cozy house-arrest situation of the former chairman of Donald Trump’s election campaign may rapidly change to confinement in a federal correctional facility if a judge in his case believes the special counsel’s new allegation of witness tampering.

Judges take a dim view of defendants who improperly pressure witnesses, though prosecutors are rarely chastised and virtually never prosecuted for similar conduct. A tampering allegation could be a devastating blow to the aggressive Manafort defense – though he has not been charged.

Manafort, who has pleaded not guilty to charges related to his failure to disclose his US lobbying work for a foreign government and to bank fraud and other financial crimes, is currently out on house arrest and a $10 million unsecured bail while he awaits trials in Virginia and Washington, D.C.

Judges view the protection of witnesses as a paramount concern of the criminal justice system and customarily come down hard on defendants who threaten, use improper pressure or clearly seek to suborn perjury.

To date, prosecutors have been particularly tough on Manafort, lodging the most serious charges against him of anyone caught up in special counsel Robert Mueller’s investigative dragnet. Many believe federal prosecutors are trying to force Manafort to testify against President Trump.

The law normally permits prosecutors, defense attorneys and even defendants themselves to communicate with potential witnesses. Prosecutors, however, often act like they own the witnesses, always lurking in the background ready to swoop in on the defense if they think witnesses are being threatened or pressured to change their testimony.

For this reason, careful defense attorneys usually warn their clients to steer clear of the witnesses. The safer route is to let defense attorneys and their investigators handle witness contact. Occasionally, though, the client gets involved with or without the permission of his lawyer.

What does Mueller’s team have on Manafort, in this instance?

An FBI affidavit submitted to the US District Court for the District of Columbia indicates that, after accessing Manafort’s cloud-based Apple account, investigators determined that he has been communicating with someone described by the FBI as “Person A” in an attempt to get “encrypted” messages to members of the “Hapsburg Group,” a group of individuals and European politicians allegedly connected to Manafort’s Ukrainian and lobbying efforts in eastern Europe.

The communication, according to the prosecutors, conveyed the message that “Basically P wants to give him a quick summary that he says to everybody (which is true) that our friends never lobbied in the US, and the purpose of the program was EU.”

The Mueller team asserts this is clearly an attempt to “suborn perjury” because Manafort and the European witnesses in question are well aware that his lobbying efforts extended to the United States. Prosecutors are saying that this is an attempt to pressure or coax the witnesses to lie in support of a false Manafort narrative.

Manafort’s aggressive defense team can be expected to fight these allegations by portraying them as another example of the overreach of Mueller’s prosecutorial team, which was recently criticized by US District Court Judge T.S. Ellis, who is presiding over charges filed against Manafort in Virginia.

These witness-tampering allegations, however, were submitted to the Washington, D.C., federal district court of Judge Amy Berman Jackson, where one of Manafort’s cases is docketed for trial. The Manafort attorneys are likely to argue that the FBI surveillance of Manafort’s “cloud storage” was done without “probable cause” and that in any event, it is not a crime to tell others what your defense in a criminal case will be.

They are likely to characterize the evidence of tampering as thin and the witness tampering accusations against Manafort as yet another improper pressure tactic to undermine the defense and force Manafort’s cooperation with the special counsel. Preparing a complex defense involving thousands of documents with an incarcerated defendant is extraordinarily difficult. That is why the new allegations could place Manafort in an exceptionally perilous position.

Federal witness tampering is a serious crime. Depending of the circumstances, it can be punished by up to 20 years in prison under 18 U.S.C. § 1512.

If the court believes there is probable cause to support such charges, Manafort would likely be incarcerated in a federal correctional facility with limited ability to communicate with anyone other than his attorneys and family members until his trials are concluded.