Citing the actual statute is a better place to start. 18 USC 793(e).
Whoever having unauthorized possession of, access to, or control over any document, writing, code book, signal book, sketch, photograph, photographic negative, blueprint, plan, map, model, instrument, appliance, or note relating to the national defense, or information relating to the national defense which information the possessor has reason to believe could be used to the injury of the United
States or to the advantage of any foreign nation, willfully communicates, delivers, transmits or causes to be communicated, delivered, or transmitted, or attempts to communicate, deliver, transmit or cause to be communicated, delivered, or transmitted the same to any person not entitled to receive it,
or willfully retains the same and fails to deliver it to the officer or employee of the United States entitled to receive it
Do we have proof that Trump took it? He certainly thinks he could have.
"I don't think you would do it," Hannity told Trump, offering him an out. But Trump replied, "I would do that," and claimed it was his "right."
www.businessinsider.com
Smith has talked to a lot of people about how the boxes containing the classified information were packed (by Trump) and has lots of text messages showing that Trump was protective of them and liked going through them himself.