I think it is important to strip the situation of political overtones (and there are plenty), and look at it strictly as a criminal matter:
"It is a federal crime to remove classified documents wrongly. And so if you are filling out that affidavit [for the search warrant] and you have to list the crime, you can list that as the crime," said Elie Honig, a former federal and state prosecutor and a CNN senior legal analyst.
"The National Archives, charged with collecting and sorting presidential material, has previously said at least 15 boxes of White House records were recovered from Trump's Mar-a-Lago resort --
including some that were classified. (
National Archives acknowledges clas...s at Mar-a-Lago after Trump left office (CNN)).
In early June, a handful of investigators made a rare visit to the property seeking more information about potentially classified material from Trump's time in the White House that had been taken to Florida. The four investigators, including Jay Bratt, the chief of the counterintelligence and export control section at the Justice Department, sat down with two of Trump's attorneys, Bobb and Evan Corcoran, according to a source present for the meeting.
....
Five days later, on June 8, Trump's attorneys received a letter from investigators asking them to further secure the room where the documents were stored.
....
In April and May, aides to Trump at Mar-a-Lago were interviewed by the FBI as part of the probe into the handling of presidential records, according to a source familiar with the matter."
FBI executes search warrant at Trump's Mar-a-Lago in document investigation (CNN)