Today on Post Reports, why the FBI searched former president Donald Trump’s Florida residence, Mar-a-Lago, and what they’re looking for.Read more:On Monday, former president Donald Trump announced that his Palm Beach, Fla., home had been searched by the FBI. No former president has ever faced a search by federal investigators like this.This is the next step in an investigation of whether Trump took classified documents with him when he left the White House. The National Archives retrieved 15 boxes of documents from Mar-a-Lago earlier this year.Matt Zapotosky, an editor at The Post who formerly covered the Justice Department, explains what federal agents were looking for and the complex calculations behind the FBI’s search.