Danchenko was a key source for the so-called dossier on Trump prepared during the 2016 campaign by former British spy Christopher Steele.

Danchenko's lead attorney, Mark Schamel, issued a statement this week suggesting that the charges against his client are false and infected with politics.

"For the past five years, those with an agenda have sought to expose Mr. Danchenko’s identity and tarnish his reputation while undermining U.S. National Security. From the moment he was inappropriately revealed, he has been the focus of unrelenting politically motivated attacks," Schamel said. "This latest injustice will not stand. We will expose how Mr. Danchenko has been unfairly maligned by these false allegations."

Trenga set a trial in the case for April 18, but there were immediate indications that the pretrial proceedings in the case could drag out due to the need to produce a large volume of documents about the underlying investigation.

"We believe that discovery is going to be fairly extensive," Assistant Special Counsel Michael Keilty told Trenga, an appointee of President George W. Bush. Keilty said a "vast" amount of classified information is also involved, which will require security clearances and other special precautions.

Another challenge is that Schamel is currently defending a client in a pharmacy fraud trial in Greeneville, Tenn. That trial is expected to run for two months, according to the lawyer who represented Danchenko at hearings last week and Wednesday, Christopher Schafbuch.

Danchenko wore a suit and tie for Wednesday's session. At his first court appearance last week, he was wearing slacks and a dress shirt after he was abruptly arrested when a plan to allow him to self-surrender was upended by what a prosecutor called "a press leak" about the case.

At that hearing, a magistrate judge decided not to put Danchenko on GPS location monitoring after prosecutors said it could wait for a day. Prosecutors did not seek to change the Russian citizen's bail conditions Wednesday, so he will remain free on bond.

Wednesday's hearing took place in a courtroom two floors below Trenga's usual one, due to a flood from a burst pipe. The incident rendered several spaces in the building unusable for the time being. Restoration crews were on site Wednesday morning with pumping equipment in a bid to resolve the issue.

Danchenko is the third person to be charged by Durham. FBI attorney Kevin Clinesmith pleaded guilty last year to a false-statement charge for altering an email sent to a colleague as part of efforts to seek a surveillance warrant against former Trump campaign foreign policy adviser Carter Page.

Two months ago, Durham charged an attorney who represented the Democratic National Committee and the Hillary Clinton campaign, Michael Sussmann, with making a false statement during a meeting with the FBI's top lawyer about allegations related to ties between Trump and Russia. Sussmann has pleaded not guilty.