Former aides to Hillary Clinton have criticised Vermont Senator Bernie Sanders for his use of private planes wile acting as a surrogate to their former boss during the 2016 campaign, and his apparent continued reliance on the form of transportation since.

Mr Sanders, who is a leading contender for the Democratic nomination in 2020, reportedly requested private jets during the 2016 campaign to act as a surrogate, to the point that it became a point of contention. Meanwhile, several high profile surrogates to the Clinton campaign were also the beneficiaries of private plane travel, including Jay-Z and Beyoncé.

Representatives for Mr Sanders have indicated that the private travel was necessary in order to make sure the Vermont senator could attend all of the events he was asked to attend for Ms Clinton.

“I’m not shocked that while thousands of volunteers braved the heat and cold to knock on doors until their fingers bled in a desperate effort to stop Donald Trump, his Royal Majesty King Bernie Sanders would only deign to leave his plush DC office or his brand new second home on the lake if he was flown around on a cushy private jet like a billionaire master of the universe,” Zac Petkanas, the director of rapid response for the Clinton campaign, told Politico in a report detailing the private plane criticism.

Since that 2016 election travel, Mr Sanders has reportedly spent at least $342,000 on private flights.

Bernie Sanders campaigns with Hillary Clinton Show all 15 1 /15 Bernie Sanders campaigns with Hillary Clinton Bernie Sanders campaigns with Hillary Clinton Democratic presidential candidate Hillary Clinton, followed by Sen. Bernie Sanders, I-Vt. arrives for a rally in Portsmouth, N.H., Tuesday, July 12, 2016. Andrew Harnik/AP Bernie Sanders campaigns with Hillary Clinton A woman holds a sign at an event where Bernie Sanders will appear with Hillary Clinton at Portsmouth High School July 12, 2016 in Portsmouth, New Hampshire. Sanders and Clinton are expected to show unity within the party and a forwarding of their agendas. Darren McCollester/Getty Bernie Sanders campaigns with Hillary Clinton Cerys Coffey, 5, of North Hampton, Massachusetts, walks along a line of supporters waiting to get into a campaign event with Democratic U.S. presidential candidates Hillary Clinton and Senator Bernie Sanders in Portsmouth, New Hampshire, U.S., July 12, 2016. Mary Schwalm/Reuters Bernie Sanders campaigns with Hillary Clinton Democratic U.S. presidential candidate Hillary Clinton and Sen. Bernie Sanders stand together during a campaign rally where Sanders endorsed Clinton in Portsmouth, New Hampshire, U.S., July 12, 2016. Brian Snyder/Reuters Bernie Sanders campaigns with Hillary Clinton Democratic U.S. presidential candidate Hillary Clinton and Sen. Bernie Sanders greet supporters during a campaign rally where Sanders endorsed Clinton in Portsmouth, New Hampshire, U.S., July 12, 2016. Brian Snyder/Reuters Bernie Sanders campaigns with Hillary Clinton Democratic U.S. presidential candidate Hillary Clinton speaks as Senator Bernie Sanders looks on after he endorsed her during a campaign rally in Portsmouth, New Hampshire, U.S., July 12, 2016. Brian Snyder/Reuters Bernie Sanders campaigns with Hillary Clinton Democratic U.S. presidential candidate Hillary Clinton (R) looks on as Senator Bernie Sanders endorses her during a campaign rally in Portsmouth, New Hampshire, U.S., July 12, 2016. Brian Snyder/Reuters Bernie Sanders campaigns with Hillary Clinton Democratic U.S. presidential candidate Hillary Clinton looks on as Senator Bernie Sanders endorses her during a campaign rally in Portsmouth, New Hampshire, U.S., July 12, 2016. Brian Snyder/Reuters Bernie Sanders campaigns with Hillary Clinton Democratic presidential candidate Hillary Clinton, followed by Sen. Bernie Sanders, I-Vt., arrives for a rally in Portsmouth, N.H., Tuesday, July 12, 2016, where Sanders endorsed Clinton for president. Andrew Harnik/AP Bernie Sanders campaigns with Hillary Clinton Sen. Bernie Sanders, I-Vt. waves as he a Democratic presidential candidate Hillary Clinton arrive for a rally in Portsmouth, N.H., Tuesday, July 12, 2016. Andrew Harnik/AP Bernie Sanders campaigns with Hillary Clinton People hold signs outside an event where Bernie Sanders will appear with Hillary Clinton at Portsmouth High School July 12, 2016 in Portsmouth, New Hampshire. Sanders and Clinton are expected to show unity within the party and a forwarding of their agendas. Darren McCollester/Getty Bernie Sanders campaigns with Hillary Clinton Supporters for Democratic presidential candidates Hillary Clinton and Sen. Bernie Sanders, I-Vt. cheer before a rally in Portsmouth, N.H., Tuesday, July 12, 2016, prior to the arrival of Clinton and Sanders. Sanders is poised to offer his long-awaited endorsement of Clinton, hoping to transfer the energy of his supporters into the party's fight against Republican Donald Trump. Andrew Harnik/AP Bernie Sanders campaigns with Hillary Clinton Supporters of Democratic presidential candidate Hillary Clinton sing the national anthem in Portsmouth, N.H., Tuesday, July 12, 2016, prior to a rally with Democratic presidential candidates Hillary Clinton and Sen. Bernie Sanders, I-Vt. Sanders is poised to offer his long-awaited endorsement of Democratic rival Hillary Clinton, hoping to transfer the energy of his supporters into the party's fight against Republican Donald Trump. Andrew Harnik/AP Bernie Sanders campaigns with Hillary Clinton Supporters of Democratic presidential candidate Hillary Clinton sing the national anthem in Portsmouth, N.H., Tuesday, July 12, 2016, prior to a rally with Democratic presidential candidates Hillary Clinton and Sen. Bernie Sanders, I-Vt. Sanders is poised to offer his long-awaited endorsement of Democratic rival Hillary Clinton, hoping to transfer the energy of his supporters into the party's fight against Republican Donald Trump. Andrew Harnik/AP Bernie Sanders campaigns with Hillary Clinton A woman holds poster for Democratic presidential candidate Hillary Clinton during a rally in Portsmouth, N.H., Tuesday, July 12, 2016, where Sen. Bernie Sanders, I-Vt. endorsed her for president. Andrew Harnik/AP

“The requests for a charter only came after the schedules were put in front of us. If a less rigorous schedule were put in front of us, we wouldn’t have needed a charter and that would have been fine for everyone involved, including Bernie,” Rania Bertrice, Mr Sanders’s former deputy campaign manager, said.

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The Sanders 2020 campaign has indicated the senator plans on using commercial air travel as much as possible during the primaries, but that chartered planes may be used if schedules require that form of travel.

In response to the criticism of Mr Sanders, Dan Pfeiffer, a former senior adviser to Barack Obama, called the attacks "petty".