Aileen M. Cannon, the Federal District Court judge assigned to preside over former President Donald J. Trump’s classified documents case, has scant experience running criminal trials, calling into question her readiness to handle what is likely to be an extraordinarily complex and high-profile courtroom clash.

Judge Cannon, 42, has been on the bench since November 2020, when Mr. Trump gave her a lifetime appointment shortly after he lost re-election. She had not previously served as any kind of judge, and because about 98 percent of federal criminal cases are resolved with plea deals, she has had only a limited opportunity to learn how to preside over a trial.

A Bloomberg Law database lists 224 criminal cases that have been assigned to her, and a New York Times review of those cases identified four that went to trial. Each was a relatively routine matter, like a felon who was charged with illegally possessing a gun. In all, the four cases added up to 14 trial days.

Judge Cannon’s suitability to handle such a high-stakes and high-profile case has already attracted scrutiny amid widespread perceptions that she demonstrated bias in the former president’s favor last year, when she oversaw a long-shot lawsuit filed by Mr. Trump challenging the F.B.I.’s court-approved search of his Florida home and club, Mar-a-Lago.

In that case, she shocked legal experts across the ideological divide by disrupting the investigation — including suggesting that Mr. Trump gets special protections as a former president that any other target of a search warrant would not receive — before a conservative appeals court shut her down, ruling that she never had legitimate legal authority to intervene.

“She’s both an inexperienced judge and a judge who has previously indicated that she thinks the former president is subject to special rules so who knows what she will do with those issues?” said Julie O’Sullivan, a Georgetown University criminal law professor and former federal prosecutor.

In theory, Judge Cannon could step aside on her own for any reason, or the special counsel, Jack Smith, could ask her to do so under a federal law that says judges are supposed to recuse themselves if their “impartiality might reasonably be questioned” — and, if she declines, ask an appeals court to order her to recuse.

There is no sign that either of them are considering taking that step, however — or what its legal basis would be.

The appeals court last year found that she was wrong about jurisdiction law, not that she was biased. And judges have previously heard litigation involving presidents who appointed them — including the Trump search warrant lawsuit, in which, notably, two of the three appeals court judges who reversed her intervention were also Trump appointees.

By bringing the charges in Florida, where most of the alleged crimes took place, instead of Washington, where the grand jury that primarily investigated the matter sat, the special counsel, Mr. Smith, avoided a potential fight over whether the case was in the right venue but ran the risk that Judge Cannon could be assigned the case.

But the chances appeared low. Under the Southern District of Florida’s practices, a computer in the clerk’s office assigns new cases randomly among judges who sit in the division where the matter arose or a neighboring one — even if the matter relates to a previous case. Nevertheless, Judge Cannon got it.

The chief clerk of the court has said that five active judges were eligible to draw Mr. Trump’s case, and that Judge Cannon’s odds of receiving it were slightly higher than others because half of her cases come from the West Palm Beach division, where Mar-a-Lago is. The clerk has also said normal procedures were followed in making the assignment.

Several lawyers who have appeared before Judge Cannon in run-of-the-mill criminal cases described her in interviews as generally competent and straightforward — and also, in notable contrast to her rulings hobbling the Justice Department after the search, someone who does not otherwise have a reputation of being unusually sympathetic to defendants.

At the same time, they said, she is demonstrably inexperienced and can bristle when her actions are questioned or unexpected issues arise. The lawyers declined to speak publicly because they did not want to be identified criticizing a judge who has a lifetime appointment and before whom they will likely appear again.

The four criminal trials that Judge Cannon presided over involved basic charges, including accusations of possession of a gun by a felon, assaulting a prosecutor, smuggling undocumented migrants from the Bahamas, and tax fraud. The four matters generated between two and five days of trial each.

The Trump case is likely to raise myriad complexities that would be challenging for any judge — let alone one who will be essentially learning on the job.

There are expected to be fights, for example, over how classified information can be used as evidence under the Classified Information Procedures Act, a national security law that Judge Cannon has apparently never dealt with before.

Defense lawyers are also likely to ask her to suppress as evidence against Mr. Trump notes and testimony from one of his lawyers. While another federal judge already ruled that a grand jury could get otherwise confidential lawyer communications under the so-called crime-fraud exception to attorney-client privilege, Judge Cannon will not be bound by that decision in determining what can be used in trial.

The judge will likely have to vet claims of prosecutorial misconduct put forward by Mr. Trump and his defense team.

“That has already been signaled in a lot of the media statements made by Trump and his lawyers,” Samuel Buell, a Duke University law professor and former federal prosecutor, said of the misconduct claims. “This is very typical, but she is a very inexperienced judge, so even if she weren’t favorable to Trump, she might hear a lot of stuff and think she is hearing stuff that is unusual even though it’s made all the time.”

And the judge will decide on challenges to potential jurors when either side claims someone might be biased for or against one of the most famous and polarizing people in the world.

Fritz Scheller, a longtime defense lawyer in Florida who has had cases in Judge Cannon’s district but not appeared before her, said in complex and high-profile cases, even the most experienced judges are forced to think on their feet to make swift decisions.

In this case, he said, the issue of how to protect the jury from being influenced by the vast media coverage alone “will be a herculean task” for any judge.

In the aftermath of the F.B.I.’s Mar-a-Lago search, Judge Cannon repeatedly sided with the man who had appointed her. She blocked investigators from having access to the classified government documents seized from him and entertained an unprecedented legal theory put forward by his lawyers that White House records could be kept from the Justice Department in a criminal investigation on the basis of executive privilege.

Eventually, a conservative appeals court panel — including two other Trump appointees — reversed her, writing in a pair of scathing opinions that she had misread the law and had no jurisdiction to interfere in the investigation. The Supreme Court let those rebukes stand without comment, and she acquiesced, dismissing the lawsuit.

It remains to be seen what she will take from the reputational damage she brought upon herself at the start of what is likely to be many decades on the bench. She could continue her pattern from last year, or she could use her second turn in the spotlight to adjudicate the documents case more evenhandedly.

While Mr. Trump and his White House lawyers put forward many young conservatives to fill judicial vacancies when he was president, Judge Cannon was unusually young and experienced. She was 38 years old and working on appellate matters as an assistant United States attorney in Florida when Mr. Trump nominated her for a lifetime appointment, and little about her legal résumé up to that point was remarkable.

Still, the Senate majority leader at the time, Mitch McConnell, Republican of Kentucky, pushed through her confirmation vote in the lame-duck session after the election. Her nomination received little attention and did not draw particular fire from Democrats; she was confirmed 56 to 21, with 12 Democrats joining 44 Republicans to vote in favor.

The daughter of a Cuban exile, she grew up in Miami and graduated from Duke University and the University of Michigan Law School. She was identifiable as ideologically conservative, having joined the Federalist Society in law school and clerked for a conservative appeals court judge.

She had been approached by the office of Senator Marco Rubio, Republican of Florida, and asked to apply to a panel he uses to vet potential judicial candidates, she wrote on her Senate Judiciary Committee questionnaire. She also interviewed with a lawyer for Senator Rick Scott, Republican of Florida, before talking to the White House, she wrote.

(The Senate’s “blue slip” practice empowers senators to block confirmation proceedings for nominees from their states, so senators wield significant power over who the White House nominates. There are currently three vacant seats on the Federal District Court in South Florida for which President Biden has made no nomination, suggesting that Mr. Rubio and Mr. Scott have not agreed to let him fill those seats with anyone acceptable to a Democratic White House.)

Judge Cannon had graduated from law school in 2008, and her 12 years as a lawyer were the minimum the American Bar Association considers necessary for a judicial nominee. A substantial majority of the bar association’s vetting panel deemed her to be merely “qualified,” though a minority deemed her “highly qualified.”

Her criminal trial experience before becoming a judge was limited.

In 2004, when she was working as a paralegal at the Justice Department’s civil rights division before going to law school, she had “assisted federal prosecutors in two federal criminal jury trials,” she wrote on the questionnaire.

From 2009 to 2012, she was an associate at the law firm Gibson Dunn, where she worked on regulatory proceedings, not criminal matters. (She wrote that she participated in two administrative trials before agencies like the Securities and Exchange Commission.)

From 2013 to 2020, she was an assistant United States attorney in Florida. While most of that time was spent on appellate work, until 2015 she had worked in the major crimes division on ​ “a wide range of federal firearms, narcotics, fraud and immigration offenses” that resulted in the conviction of 41 defendants, she wrote. Most of those cases, however, ended in plea deals: She tried just four of them to a jury verdict, she wrote.

She was the lead counsel for two of those cases — both involving a felon charged with possessing a firearm, she wrote, and served as assistant to the main prosecutor in the other two cases, one of which she said involved possession of images of child sexual exploitation.

Other parts of Judge Cannon’s questionnaire answers put forward few experiences or accomplishments that clearly distinguished her as seasoned and demonstrably ready for the powers and responsibilities of a lifetime appointment to be a federal judge.

It asked, for example, for every published writing she had produced. She listed 20 items. Of those, 17 were pieces she had written in the summer of 2002 as a college intern at The Miami Herald’s Spanish-language sister publication, El Nuevo Herald, with headlines like “Winners in the Library Quest Competition.” The other three were articles published on Gibson Dunn’s website describing cases the firm had handled, each of which had three other co-authors.

The questionnaire also asked her to provide all reports, memorandums and policy statements she had written for any organization, all testimony or official statements on public or legal policy she had ever delivered to any public body, and all her speeches, talks, panel discussions, lectures or question-and-answer sessions.

“None,” she wrote.

Kitty Bennett, Susan C. Beachy and Matthew Cullen contributed reporting.

Leave a Reply

Your email address will not be published. Required fields are marked *