Mr. Nauta’s plea was entered for him by his lawyer, Stanley Woodward Jr., at a brief arraignment in Federal District Court in Miami. Mr. Woodward was accompanied at the hearing by a local Florida lawyer who will be helping in the case, Sasha Dadan.

A 40-year-old Navy veteran from Guam, Mr. Nauta was charged with Mr. Trump last month in a 38-count indictment with conspiracy, making false statements and withholding documents. He was not arraigned with Mr. Trump on June 13 because Mr. Woodward, who is based in Washington, had not yet hired a lawyer licensed to practice in Florida.

Ms. Dadan, a former public defender, has limited experience with the federal courts — her name does not appear at all in PACER, the nationwide database of federal cases — but she has handled numerous local cases in Fort Pierce, Fla. That is where Judge Aileen M. Cannon, who is overseeing Mr. Trump’s prosecution, is based and where the former president’s trial with Mr. Nauta may eventually be held.

Ms. Dadan has also been active in Republican politics in recent years, mounting an unsuccessful campaign for the Florida House in 2018.

The indictment against Mr. Trump and Mr. Nauta was filed by the office of the special counsel Jack Smith. It describes how Mr. Nauta repeatedly moved boxes at Mr. Trump’s request in and out of a storage room at Mar-a-Lago, the former president’s private club and residence in Florida, during a critical period: the weeks between the issuance of a subpoena in May 2022 demanding the return of all classified documents in Mr. Trump’s possession and a visit to Mar-a-Lago soon after by federal prosecutors seeking to enforce the subpoena and collect any relevant materials.

According to the indictment, Mr. Nauta removed 64 boxes from the storage room during those weeks but only brought back about 30, with the rest unaccounted for. All of this took place, the indictment says, before one of Mr. Trump’s lawyers, M. Evan Corcoran, began to sort through the material kept in the storage room in an effort to find any remaining classified material and turn it over to the government.

Mr. Nauta’s arraignment — a brief and largely ceremonial procedure — had none of the circuslike atmosphere that marked Mr. Trump’s own arraignment in Miami. The hearing in front of Magistrate Judge Edwin G. Torres lasted about 10 minutes as Mr. Woodward did little more than enter Mr. Nauta’s plea and request a jury trial.

Mr. Nauta, who served as one of Mr. Trump’s White House valets before going to work for him at Mar-a-Lago, is now in the delicate position of being both the former president’s co-defendant in a high-stakes federal prosecution and one of his most intimate employees. Complicating matters, Mr. Trump is under a court order not to discuss the facts of the indictment with more than 80 people involved in the case — including Mr. Nauta, whose job is to shadow the former president everywhere he goes and to cater to his various whims and needs.

Well before the indictment was filed, the government had been trying to get Mr. Nauta to turn on Mr. Trump and cooperate with their investigation. As early as last fall, prosecutors in Washington ratcheted up the pressure on Mr. Nauta and Mr. Woodward, saying they were skeptical of Mr. Nauta’s account about moving boxes for Mr. Trump.

Two weeks ago, prosecutors working for Mr. Smith asked Judge Cannon to push the start of the trial back until Dec. 11. Mr. Trump’s lawyers have until Monday to respond to the government’s request and suggest their own schedule.

The timing of the trial could be hugely consequential, particularly if Judge Cannon allows it to take place after the 2024 election. Should that happen and should Mr. Trump — the current front-runner for the Republican nomination — win the race, he could have his attorney general simply drop the case in its entirety.