The Service is tasked with protecting high-ranking government officials and presidential candidates (among other duties) like Trump. Since this protection is mandatory, it’s common practice for the Service to reimburse campaigns for travel expenses. But it looks like the $1.6 million the Service recently paid the Trump campaign went right back to Trump’s business interests, according to Politico.

The business mogul and his security detail regularly fly on the Trump-owned jet service, TAG Air. The firm also manages Trump’s fleet of private planes. So the money the Service pays back goes right back to his business. Politico reviewed Federal Election Commission filings and found that TAG has already made $6 million off Trump’s campaign.

For comparison, Democratic candidate Hillary Clinton charters planes from a private company called Executive Fliteways, one where the Clintons do not have any ownership interest, Politico reported.

It’s not the only way that Trump has been profiting from his White House run.

Last week, he finally admitted President Obama was born in the United States at his hotel in Washington, D.C., earning free media coverage for what CNN’s Jake Tapper later called a “political rick roll.” Trump’s campaign has spent major sums on rent at his hotels and buying copies of his own books, too. He’s even previously stated that he may wind up actually making money from his presidential bid.