Why the FBI's search of Mar-a-Lago feels like a shift in the tectonic legal plates

A legal barrier of sorts has been broken: The FBI obtained and executed a search warrant on the home of a former president of the United States. This represents the kind of maiden legal voyage by the Department of Justice that has been prompted by the conduct of Donald J. Trump.

There are few things we know — and much we don’t know — about Monday’s search of Mar-a-Lago, Trump’s Florida home. Let’s start with what we do know.

First, the decision to request a search warrant was undoubtedly vetted through the uppermost ranks of the Justice Department, likely all the way through Deputy Attorney General Lisa Monaco and Attorney General Merrick Garland.

Second, a federal judge authorized this search. When the FBI, an agency within the Justice Department, decides that a search warrant should be pursued as part of a criminal investigation, agents will draft and swear to the truthfulness and accuracy of an affidavit in support of a search warrant. That sworn affidavit will include evidence the agents believe satisfies the burden of proof for warrants to be issued: probable cause.

Whereas precisely defining what evidence satisfies the probable cause standard is challenging, we know it lies somewhere between “reasonable articulable suspicion,” the standard set by the Supreme Court for an officer to “stop and frisk” an individual, and a preponderance of the evidence, that is, more likely than not. Importantly, the preponderance of the evidence standard is higher than the probable cause standard (which is the standard to issue search warrants, arrest warrants and grand jury indictments).