WASHINGTON (CN) – For the second trial of President Donald Trump’s former campaign chair, prosecutors pushed Monday to rely on the testimony of a lawyer who handled Paul Manafort’s foreign agent registration filings.

Already convicted of eight financial crimes in Virginia, Manafort is slated to stand trial in Washington later this month for having knowingly made false statements on his Foreign Agent Registration Act paperwork.

Indicted by special counsel Robert Mueller, who is investigating Russian interference in the 2016 election, Manafort also faces several charges related to his failure to register as a foreign agent while lobbying on behalf of a pro-Kremlin political party in Ukraine.

The testimony of a lawyer who handled Manafort’s filings could be pivotal to the government’s case, but Manafort wants the evidence barred from trial.

Attorney-client privilege typically shields attorneys from having to disclose what their clients tell them in confidence, but there are some exceptions to the privilege rule, including when an investigative subject lies to his attorney, after which the attorney inadvertently passes those lies on to the government.

U.S. Chief District Judge Beryl Howell ruled in October last year that the crime-fraud exception applies since Manafort “likely violated federal law by making, or conspiring to make materially false statements and misleading omissions” on Foreign Agent Registration Act submissions and that the attorney could be compelled to answer seven specific questions.

The lawyer is not named in the government’s court filings, but prosecutors identified Akin Gump attorney Melissa Laurenza in an exhibit filed late last month in their bid to access some of the attorney’s communications with Manafort.

Laurenza has also been named as a potential witness in the upcoming case.

On Monday prosecutor Andrew Weissmann argued in a court filing that Manafort offered no factual basis to disturb Howell’s ruling.

“The government believes that, even if the ruling does not formally constitute the law of the case, it is entitled to deference and should be followed herein,” the brief says.

Weissmann also cited the doctrine of issue preclusion, which bars Manafort from relitigating an issue that Howell already put to rest.

Manafort previously objected on the basis that he had not received the relevant grand jury pleadings, but his defense attorneys have since acknowledged that he has an unredacted copy of Howell’s opinion, transcripts of the proceedings before Howell, and the government’s filings – including FBI notes detailing interviews with the attorney.

Unless Manafort can present new evidence that his attorney’s testimony is privileged, Weissmann said U.S. District Judge Amy Berman Jackson – who is presiding in Washington over Manafort’s criminal case – should defer to Howell’s ruling on the matter.

“The legal issues carefully considered by Chief Judge Howell are identical to those raised now, and revisiting them in the absence of a compelling reason to do so would contravene principles of judicial economy, consistency, and comity,” the brief says.

Manafort’s attorney Richard Westling responded to the filings late Monday night, arguing that Howell’s ruling does not constitute the law of the case, and that Jackson is not obligated to adhere to it.

“Importantly, the prior ruling determined the grand jury’s ability to obtain the evidence, but did not resolve trial admissibility,” the response says.

Westling accused the prosecution of having failed to disclose whether the attorney’s testimony is expected to extend beyond what Howell authorized, as well as more generally what the lawyer will say.

Westling also noted that Howell’s opinion did not address whether prosecutors could review additional emails Manafort exchanged with the attorney, which the special counsel’s office requested on Aug. 15.

In a separate filing that also appeared Monday night, defense attorney Kevin Downing said the defense will not argue that Manafort faced selective prosecution.

Prosecutors had asked the court to bar Manafort from making such arguments during trial, but Downing asked the court instead to allow the defense to elicit testimony from government witnesses that would illustrate that Foreign Agent Registration Act requirements are so vague that even the attorneys who handle submissions can’t decipher them.

Downing calls the “scarcity of enforcement actions” telling, noting that why the Justice Department has instigated only seven prosecutions under the law since 1966.

Jury selection for Manafort’s second criminal trial is scheduled to begin Sept. 17 in Washington, with opening arguments in the trial slated for Sept. 24.