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WASHINGTON — In a major shake-up to Bernie Sanders' just-launched presidential bid, some of his top strategists have left the campaign.

Tad Devine, Mark Longabaugh and Julian Mulvey, partners in a political consulting firm who all played leading roles in Sanders' 2016 campaign for the White House, are parting ways with the senator, citing creative differences.

"The entire firm has stepped away. We're leaving the campaign," Longabaugh told NBC News on Tuesday. "We just didn't have a meeting of the minds."

Devine, a veteran Democratic presidential operative, was a familiar presence on TV in 2016 as Sanders' chief strategist, responsible for setting the early direction of the campaign when few other Washington insiders believed the little-known Vermont independent could be a serious contender for the Democratic presidential nomination.

Longabaugh helped design and implement the campaign's delegate-hunting roadmap and negotiated with key outside players like the Democratic National Committee on issues like debates.

Mulvey helped craft the firm's ads for Sanders, including his best-known commercial, which featured the Simon & Garfunkel song "America."

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All together, the firm produced 275 television, radio and digital ads for that campaign and was involved in much of the campaign's top decision-making.

"The campaign appreciates all the good work DML has done and wishes them well," Sanders' new campaign manager, Faiz Shakir, said in a statement, referring to the name of their firm.

The firm had been hiring staff in anticipation of Sanders' 2020 campaign, and produced the video Sanders used to announce his campaign last week.

"We are leaving because we believe that Sen. Sanders deserves to have media consultants who share his creative vision for the campaign," Devine, Longabaugh and Mulvey said in a joint statement.

Both sides insist the departure was amicable, but some tensions between Sanders and Devine were evident in the final days of the 2016 primary campaign when Sanders pressed on with his run after it became clear he couldn't win the nomination against Hillary Clinton.

More recently, Devine has faced scrutiny for his consulting work years ago in Ukraine with former Trump campaign chairman Paul Manafort, who has pleaded guilty to financial crimes and is awaiting sentencing.

And the firm has come under criticism from Sanders allies for the money they made from Sanders and his small-dollar fundraising machine in 2016, with $5.3 million in direct payments to the firm from the campaign, according to the Federal Election Commission reports.

Meanwhile, Sanders has pledged to diversify the top ranks of his campaign.

"We have been criticized, correctly so, for running a campaign that was too white and too male-oriented, and that is going to change," Sanders said in a recent interview with The Young Turks.

Along with Jeff Weaver, Sanders' 2016 campaign manager, and a small handful of others, including his wife Jane, the consultants have been a core part of the Sanders inner circle for years.

When Weaver published his campaign memoir last summer, they hosted a book party for him at a bar in Washington, where Sanders spoke.

On Tuesday morning, they called Weaver, who is now serving as a top counselor to Sanders' 2020 bid, to say they could not see a way of working together again.

It's not uncommon for presidential candidates to part ways with top aides before running again, and Sanders is likely now more confident in his own abilities to lead a campaign than he was four years ago.

The Sanders campaign declined to immediately say who would replace the three men in either their roles as admakers or strategists.