Several legal specialists in criminal law pointed to this challenge as a likely explanation for why the Justice Department might hesitate to charge a former president and is instead allowing the larger investigation to continue.

“Proving something by preponderance of the evidence to a judge is a very different thing than proving it beyond a reasonable doubt to a jury,” said David Alan Sklansky, a Stanford University criminal law professor. “It’s reasonable to expect that prosecutors would be particularly careful not to jump the gun when you’re talking about charging a former president with a crime.”