Donald Trump used $55,000 of campaign funds to buy thousands of copies of his own book from a retail store, a purchase that could be illegal, the Daily Beast reported Wednesday.

The funds went toward buying his book, Crippled America: How to Make America Great Again, from Barnes & Noble — copies of which were handed out as gifts at the Republican National Convention in Cleveland, according to the Daily Beast. The site reported that the $55,000 purchase would amount to 3,500 copies of the hard copy version of the book, or 5,000 copies of the paperback version, which was renamed Great Again: How to Fix Our Crippled America.

If Trump accepts royalties from the publisher on the book, purchasing that many copies would amount to shifting donor funds back into his own bank account, an illegal practice, campaign finance experts told the Daily Beast.

"It's fine for a candidate's book to be purchased by his committee, but it's impermissible to receive royalties from the publisher," Paul Ryan, deputy executive director of the Campaign Legal Center, told the site. "That amounts to an illegal conversion of campaign funds to personal use."

The book purchasing news came two days after the Huffington Post reported that Trump hiked up the rent on the office space his campaign is utilizing for its headquarters at Trump Tower in New York — which Trump himself owns.

The Huffington Post reported that Trump raised the rent almost five-fold to to $169,758 a month — an increase that came as Trump shifted to raising money from donors, rather than self-financing his campaign.

According to his July fundraising report filed to the Federal Elections Commission, Trump has spent at least $7.7 million of his campaign funds toward Trump-owned companies, as well as to his children, who have been a staple on the campaign, Vice reported.

Trailing Hillary Clinton badly in the polls, it's possible that Trump's campaign will now find itself on the receiving end of attacks from the Democratic nominee over his campaign expenses.

"If I was a donor, I'd want answers," an RNC member told the Huffington Post. "If they don't have any more staff, and they're paying five times more? That's the kind of stuff I'd read and try to make an (attack) ad out of it."