Bernie Sanders demanded a private jet for his 2016 campaign travel for Hillary Clinton, her bitter former staffers revealed in the wake of the Vermont senator's presidential announcement.

'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 D.C. 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, who was the director of rapid response for the Clinton campaign, told Politico.

The staffers were quick to point out Sanders railed against the fossil fuel industry in his campaign announcement video last week.

Bernie Sanders demanded a private jet for his 2016 campaign travel for Hillary Clinton, her bitter former staffers revealed after he announced his 2020 bid

There are linger bad feelings between Hillary Clinton and Bernie Sanders' teams after the bitter 2016 primary; Sanders endorsed her in July 2016 after he ended his bid for the Democratic nomination

Their criticism points to lingering hard feelings from the 2016 primary election where many Clinton staffers believe Sanders stayed in the contest too long when he had no hope of securing the nomination and criticized Clinton too much, contributing to her defeat.

He waited a month to endorse her after she secured the nomination and the two sides fought it out about his speaking slot at the Democratic National Convention: the Clinton team tried to put him on early - before the networks started airing the addresses - but his side fought back and secured him a primetime speaking slot.

There are hard feelings on Sanders' side too, particularly after hacked emails from the Democratic National Committee - released by Wikileaks - showed a concentrated effort on behalf of some high-level party officials to secure the nomination for Clinton over Sanders.

Michael Briggs, Sanders' 2016 campaign spokesman, called Clinton and her team 'total ingrates.'

'You can see why she's one of the most disliked politicians in America. She's not nice. Her people are not nice,' he told Politico. '[Sanders] busted his tail to fly all over the country to talk about why it made sense to elect Hillary Clinton and the thanks that [we] get is this kind of petty stupid sniping a couple years after the fact.'

'It doesn't make me feel good to feel this way but they're some of the biggest a**holes in American politics,' he added.

In the two years since that bitter election, Sanders still used private jets, spending at least $342,000 on the flights, Politico noted.

Those costs will come under greater scrutiny with his decision to again seek the Democratic presidential nomination.

Sanders travel was a huge point of contention with Clinton staffers, several of whom told the news website they urged commercial travel where possible but the senator's team insisted he need a private plane to accommodate the schedule the Clinton team wanted him to follow.

Sanders' flights - usually on a Gulfstream plane - cost the Clinton at least $100,000 in total.

'We would try to fight it as much as possible because of cost and availability of planes, but they would request [a jet] every time,' one souce told Politico. 'We would always try to push for commercial. ... At the campaign, you're constantly trying to save like 25 cents.'

'At that time, getting him on board - no pun intended - and his followers engaged for her, was a big priority,' said one former Clinton staffer.

Sanders spokesperson Arianna Jones told Politico it was physically impossible to get the senator to all of the event locations quickly without a private jet, especially since he was going to a lot of smaller locations with limited commercial options.

Bernie Sanders boards a plane in Denver in February 2016

HUG IT OUT: Clinton and Sanders hug when he endorsed her in New Hampshire in July 2016

Sanders at the 2016 Democratic National Convention

'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,' she 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.'

In the final three months of the 2016 campaign, Sanders held 39 rallies in 13 states on Clinton's behalf.

Rania Batrice, who was Sanders' deputy campaign manager, said the Clinton team would propose a schedule for him and 'at no point did I ever say 'he has to have a private plane for the sake of having a private plane.'

'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,' she said, later adding: 'Bernie worked his ass off on behalf of Hillary Clinton and the campaign.'

Sanders also flew private in the 2018 midterms when he traveled to help Democratic candidates.

He spent nearly $300,000 on private air travel in October so he could speak in nine battleground states.

The Sanders campaign purchased nearly $5,000 in carbon offsets to balance out the emissions produced from the travel, his campaign told Fox News in December.

As to whether Sanders will fly private or commercial for his 2020 campaign, Jones told Politico he 'will be flying commercial whenever possible. The campaign will consider the use of charter flights based on a variety of factors, including security requirements, logistics, and media interest in traveling with the senator.'