Some of Bernie Sanders' top strategists are splitting with the populist left-wing senator's 2020 presidential campaign over creative differences.

The media consulting firm Devine Mulvey Longabaugh – run by Tad Devine, Julian Mulvey and Mark Longabaugh – told Sanders on Tuesday that they were walking away from the senator's campaign efforts after helping him lead a stunning primary challenge of Hillary Clinton in 2016.

"There were differences in a creative vision," Longabaugh said in an interview with CNBC. "We want to leave on a very positive note and we are proud of the work we've done on the campaign. It was just clear, however, that we weren't in sync."

Longabaugh declined to provide details about the specific creative differences. Longabaugh also said he told Sanders that he would be happy to offer advice in the future.

"I told the senator this morning that if he ever wanted to call on me for guidance I would be glad to provide that. I think everybody was kind of sad about it," he added.

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Sanders officially launched his presidential campaign last week. He will continue to push populist liberal policies such as Medicare for all and a $15 federal minimum wage, which have become more mainstream in the Democratic Party since his insurgent primary run in 2016.

In a public statement, the firm said it is proud of its previous work with Sanders and acknowledged they helped produce 275 television, radio and digital during his last run for president. The group had helped produce one of the Sanders 2020 campaign roll-out videos.

Sanders 2020 campaign manager Faiz Shakir weighed in with a statement, too: "The campaign appreciates all the good work DML has done and wishes them well."

It's not clear what's next for Devine Mulvey Longabaugh as several Democrats, including Sens. Elizabeth Warren and Kamala Harris, battle for the chance to take on President Donald Trump in 2020.

Longabaugh said the firm has not been in touch with another 2020 campaign, but he did not rule anything out.

"We haven't to spoken anyone," he said.

Then, when pressed on whether the firm is interested in backing another candidate's organization, Longabaugh responded: "I'm not going to go there."