Sen. Bernie Sanders, I-Vt., often requested a private jet to travel to events while campaigning for Hillary Clinton in the 2016 election, according to former Clinton staffers.

Sanders has continued using a private jet in the two years since the election, spending almost $350,000 on flights, according to Politico. The former Clinton campaign workers accused the septuagenarian socialist senator of hypocrisy, juxtaposing his fondness for jets with his rhetoric regarding fossil fuels and wealth.

It's common for candidates to fly in private jets. But Sanders’ decision to travel via private jet, and the carbon footprints of the flights, is certain to be scrutinized during his 2020 bid.

During the 2016 campaign, Clinton staffers said they had preferred that Sanders mostly fly commercial. Sanders staffers told the Clinton campaign that the senator could not maintain the campaign schedule requested by Clinton’s team if he did not fly private.

“That’s why chartered flights were used: to make sure Sen. Sanders could get to as many locations as quickly as possible in the effort to help the Democratic ticket defeat Donald Trump,” Sanders spokesperson Arianna Jones said.

“Sen. Sanders campaigned so aggressively for Secretary Clinton, at such a grueling pace, it became a story unto itself, setting the model for how a former opponent can support a nominee in a general election.”

Jones said Sanders attended 29 rallies in 13 states in the the three months before Election Day. Sanders’ private flights cost the Clinton campaign at least $100,000 total.

“At no point did I ever say ‘he has to have a private plane for the sake of having a private plane,’” Rania Batrice, Sanders’ deputy campaign manager, said.