With the Iowa caucuses less than 50 days away, one of GOP presidential candidate Vivek Ramaswamy's top political advisers is leaving to work for former President Donald Trump's campaign, according to multiple sources familiar with the move.

Brian Swensen, who served as Ramaswamy's national political director since the spring and was a key player in the campaign's work in New Hampshire, confirmed to CBS News he is leaving and directed further questions about his future role to the Trump campaign.

"We love Brian," Tricia McLaughlin, Ramaswamy's communications director, told CBS News. "It's a good move for Brian and we're happy for him." 

News of Swensen's departure comes at a critical time for Ramaswamy, who has failed to recapture the momentum he had over the summer. 

Polls in Iowa and New Hampshire show the Ohio entrepreneur in the single digits, lagging far behind Trump. Ramaswamy has largely fallen out of the second tier of candidates, which now includes former U.N. Ambassador Nikki Haley and Florida Gov. Ron DeSantis.

Michael Biundo, a recently hired senior campaign official who ran Rick Santorum's campaign in 2012, will be absorbing much of Swensen's duties, according to McLaughlin. She said that the move was amicable and that the timing of Swensen's departure was not a surprise to the campaign. The Messenger first reported on Swensen's plans to depart.

It is unclear what Swensen's role will be within the Trump campaign, but he is a close ally of Susie Wiles, a senior Trump adviser. They worked together on Rick Scott's 2010 gubernatorial race, DeSantis' gubernatorial race in 2018 and Trump's own reelection campaign in 2020.

Multiple sources told CBS News that Thursday will be Swensen's last day with the campaign. The move comes just weeks after the Ramaswamy campaign announced it was sending all staffers from its Ohio headquarters to Iowa and New Hampshire.

Despite his grim polling numbers, Ramaswamy has rejected assertions that his campaign has lost momentum. 

"I'm fully confident we're going to be successful, especially in those early states, Iowa, New Hampshire, able to beat expectations. We're sitting exactly where I want to be and I'm confident that we have the momentum ahead of us to be the nominee and more importantly to win this election in a landslide," he told reporters earlier this month in Iowa.