On the raid – Alex Leary, Aruna Viswanatha and Sadie Gurman in WSJ:

‘Monday’s search came after weeks of internal deliberation among senior Justice Department and FBI officials and marked an escalation of their investigation into Mr. Trump’s handling of classified material, people familiar with the matter said.
The controversy began after Mr. Trump left office, when the National Archives and Records Administration reached out to his team to ask for what it thought were missing records. All official documents are required to be turned over under the Watergate-era Presidential Records Act.
The Archives in January retrieved 15 boxes of documents and other items from Mar-a-Lago.
The boxes contained some documents archives officials described only as “classified national security information,” prompting them to refer the matter to the Justice Department for investigation.’

Read the article here.

National Security Information probably means highly classified US operations abroad, as have been reported by NYT.
Trump could have taken this classified information with him as part of overall clumsiness. But without thinking of grotesque conspiracy theories, there might be other reasons for this.

Who knows, maybe he is thinking of becoming the new Snowden, and the DoJ and FBI launched a pre-emptive strike. And if not the new Snowden, maybe just an agent for a foreign country, as an attempt at a new career.