Donald J. Trump regularly boasts that he is self-funding his presidential bid, but new campaign finance filings show that he is also shifting plenty of money back to himself in the process.

According to documents submitted to the Federal Election Commission, Mr. Trump, whose campaign has just $1.3 million cash on hand, paid at least $1.1 million to his businesses and family members in May for expenses associated with events and travel costs. The total represents nearly a fifth of the $6 million that his campaign spent in the month.

The spending raised eyebrows among campaign finance experts and some of Mr. Trump’s critics who have questioned whether the presumptive Republican nominee, who points to his business acumen as a case for his candidacy, is trying to do what he has suggested he would in 2000 when he mulled making an independent run: “It’s very possible that I could be the first presidential candidate to run and make money on it.”