Donald Trump used his campaign funds to buy thousands of copies of his own book at retail cost, simultaneously diverting donor money back into his pockets while artificially boosting his sales figures. It’s a tactic that may be illegal, campaign finance experts say.

On May 10, the Trump campaign paid Barnes & Noble $55,055, according to a filing with the Federal Election Commission. That amounts to more than 3,500 copies of the hardcover version of Crippled America: How to Make America Great Again, or just over 5,000 copies of the renamed paperback release, Great Again: How to Fix Our Crippled America.

A spokesperson for the Republican nominee told The Daily Beast the books were purchased “as part of gifting at the convention, which we have to do.” Sure enough, delegates in attendance at the Republican National Convention in Cleveland in July were given canvas tote bags, stamped with the Trump slogan, and filled with copies of Crippled America, as well as Kleenex and Make America Great Again! cups, hats, and T-shirts. Delegates were also given plastic fetus figurines…

“It’s fine for a candidate’s book to be purchased by his committee, but it’s impermissible to receive royalties from the publisher,” Ryan said. “That amounts to an illegal conversion of campaign funds to personal use. There’s a well established precedent from the FEC that funds from the campaign account can’t end up in your own pocket.”