Bernie Sanders spent more on private jet travel in three months than his closest competitors in the Democratic presidential race.

Federal Election Commission filings that the presidential campaigns submitted on Friday for October through December reveal that the socialist Vermont senator's campaign spent $1.2 million on private air travel through charter flight companies Advanced Aviation Team and Apollo Jets.

Former Vice President Joe Biden, 77, spent the second-most on private jets, $1 million, through Advanced Aviation. The campaign for Massachusets Sen. Elizabeth Warren, 70, spent about $721,000 on private jets through Advanced Aviation. The private plane bill for former South Bend, Indiana, Mayor Pete Buttigieg, 38, was $324,000 through Advanced Aviation, EvoJets, Solairus Aviation, and Vertivue Air Charters.

Former New York City mayor and billionaire businessman Michael Bloomberg, 77, spent about $700,000 on private jet travel from his late November campaign launch through the end of December.

Sanders was long well-known for flying coach, but after he endorsed former rival Hillary Clinton in 2016, he reportedly "repeatedly requested and received" a private jet to campaign on behalf of his former Democratic primary rival. The requests for a fuel-guzzling vehicle became a joke among Clinton staff, since Sanders had railed against fossil fuel companies in his campaign.

The Vermont senator was scheduled to take a private jet to Iowa for a midweek rally in Iowa during the Senate impeachment trial, an attempt to get around being stuck in Washington during a critical time before the critical first-in-the-nation Iowa caucuses. But due to scheduling conflicts with the trial, his trip was canceled.

His campaign (as well as those for Warren, Bloomberg, and Biden) says that it offset emissions from travel activities in part by buying credits from companies that support programs indented to reduce total global emissions, such as by developing renewable energy sources or capturing carbon out of the air.

Buttigieg faced criticism last year for leading the field in private jet travel in the first half of 2019, risking the newcomer to the national stage looking elitist before he surged in early state polls.