The U.S. Secret Service has paid the Donald Trump Donald John TrumpBubba Wallace to be driver of Michael Jordan, Denny Hamlin NASCAR team Graham: GOP will confirm Trump's Supreme Court nominee before the election Southwest Airlines, unions call for six-month extension of government aid MORE campaign about $1.6 million to cover the cost of flying its agents with the GOP presidential nominee, Politico reports.

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It is customary for Secret Service to reimburse campaigns for the cost of traveling with presidential candidates. It has reimbursed Hillary Clinton Hillary Diane Rodham ClintonJoe Biden looks to expand election battleground into Trump country Biden leads Trump by 12 points among Catholic voters: poll The Hill's Campaign Report: Biden goes on offense MORE's campaign $2.6 million so far in this presidential cycle.

But because one of Trump's companies, TAG Air Inc., owns the plane he travels on, the government is effectively paying him.

The Clinton campaign has largely relied on chartered planes from an outside private company.

A Politico analysis found that through the end of August, Trump's campaign has spent at least $8.2 million at Trump's businesses, including payments for renting event venues and office space.