NEW YORK, United States (AP) — Mounds of paper piled on his desk. Framed magazine covers and keepsakes lining the walls. One of Shaquille O’Neal’s giant sneakers displayed alongside football helmets, boxing belts and other sports memorabilia crowding his Trump Tower office and limiting table space.

Well before he entered politics, former President Donald Trump had a penchant for collecting. And that lifelong habit — combined with his flip disregard for the rules of government record keeping, his careless handling of classified information, and a chaotic transition born from his refusal to accept defeat in 2020 — have all culminated in a federal investigation that poses extraordinary legal and political challenges.

The search of Trump’s Mar-a-Lago club earlier this month to retrieve documents from his White House years was an unprecedented law enforcement action against a former president who is widely expected to run for office once again. Officials have not revealed exactly what was contained in the boxes, but the FBI has said it recovered 11 sets of classified records, including some marked “sensitive compartmented information”, a special category meant to protect secrets that could cause “exceptionally grave” damage to US interests if revealed publicly.

Why Trump refused to turn over the seized documents despite repeated requests remains unclear. But Trump’s flouting of the Presidential Records Act, which outlines how materials should be preserved, was well-documented throughout his time in office.

He routinely tore up official papers that later had to be taped back together. Official items that would traditionally be turned over to the National Archives became intermingled with his personal belongings in the White House residence. Classified information was tweeted, shared with reporters and adversaries — even found in a White House complex bathroom.

John Bolton, who served as Trump’s third national security adviser, said that, before he arrived, he’d heard “there was a concern in the air about how he handled information. And as my time went on, I could certainly see why”.

Others in the Trump Administration took more care with sensitive documents. Asked directly if he kept any classified information upon leaving office, former Vice-President Mike Pence told The Associated Press on Friday, “No, not to my knowledge.”

The investigation into Trump’s handling of documents comes as he’s facing mounting legal scrutiny on multiple fronts. A Georgia investigation into election interference has moved closer to the former president, with former New York City Mayor Rudy Giuliani, a top defender, informed earlier this month that he is a target of a criminal probe.

Few legal threats have galvanised Trump and his most loyal supporters like the Mar-a-Lago search. The former president and his allies have argued the move amounts to political persecution, noting the judge who approved the warrant has given money to Democrats. The judge, however, has also supported Republicans. And White House officials have repeatedly said they had no prior knowledge of plans to search the estate.

Trump allies have tried to claim the presidency granted him unlimited power to unilaterally declassify documents without formal declaration. But David Laufman, the former chief of the Justice Department’s counterintelligence section, said that’s not how it works.

“It just strikes me as a post hoc public affairs strategy that has no relationship to how classified information is in fact declassified,” said Laufman, who oversaw the investigation into Hillary Clinton’s personal e-mail server during her tenure as secretary of state. While he said it is true that there is no statute or order that outlines procedures the president must abide by to declassify information, “at the same time it’s ludicrous to posit that a decision to declassify documents would not have been contemporaneously memorialised in writing.”

It’s “not self-executing,” he added. “There has to be some objective, contemporaneous, evidence-based corroboration of the claims that they’re making. And of course there won’t be because they’re making it all up.”

The decision to keep classified documents at Mar-a-Lago — a property frequented by paying members, their guests and anyone attending the weddings, political fundraisers, charity dinners and other events held on site — was part of a long pattern of disregard for national security secrets. Former aides described a “cavalier” attitude toward classified information that played out in public view.

There was the dinner with then-Japanese Prime Minister Shinzo Abe on Mar-a-Lago’s patio, where fellow diners watched and snapped cellphone photos as the two men reviewed details of a North Korean missile test.

There was the time Trump revealed highly classified information allegedly from Israeli sources about Islamic State militants to Russian officials. And there was the time he tweeted a high-resolution satellite image of an apparent explosion at an Iranian space centre, which intelligence officials had warned was highly sensitive. Trump insisted he had “the absolute right” to share it.

Former White House press secretary Stephanie Grisham said Trump was “careless” with sensitive and classified information and “seemed never to bother with why that was bad.”

Grisham recalled one incident involving Conan, a US military dog hailed as a hero for his role in the raid that killed Islamic State leader Abu Bakr al-Baghdadi. She said that before the dog’s arrival at the White House, staff had received a briefing in which they were told the dog could not be photographed because the images could put his handlers in danger. But when the dog arrived, Trump decided he wanted to show it off to the press.

“Because he wanted the publicity, out went Conan,” she said. “It’s an example of him not caring if he put lives in danger. … It was like its his own shiny toy he’s showing off to his friends to impress them.”

Bolton said that, during his time working for Trump, he and others often tried to explain the stakes and the risks of exposing sources and methods.

“I don’t think any of it sank in. He didn’t seem to appreciate just how sensitive it was, how dangerous it was for some of our people and the risks that they could be exposed to,” he said. “What looks like an innocuous picture to a private citizen can be a gold mine to a foreign intelligence” entity.

“I would say over and over again, ‘This is really sensitive, really sensitive.’ And he’d say, ‘I know’ and then go and do it anyway.”

Bolton said that top intelligence officials would gather before briefings to discuss how best to handle sensitive subjects, strategising about how much needed to be shared. Briefers quickly learned that Trump often tried to hang onto sensitive documents, and would take steps to make sure documents didn’t go missing, including using iPads to show them to him.

“Sometimes he would ask to keep it and they’d say, ‘It’s really sensitive.’ Sometimes he just wouldn’t give it back.”

Bolton said he doubted that Trump had taken documents for nefarious reasons, and instead thought Trump likely considered them “souvenirs” like the many he’d collected through his life.

“I think he just thought some things were cool and he wanted them,” Bolton said. “Some days he liked to collect french fries. Some days he liked to collect documents. He just collected things.”