Ledyard King and Fredreka Schouten

USA TODAY

A key player in the Koch brothers' inner political circle will work directly on Sen. Marco Rubio’s presidential campaign, bringing deep connections to the brothers' vast network of donors and experience helping oversee their sophisticated political operation.

Republican power brokers Charles and David Koch haven't endorsed a GOP primary candidate, but Marc Short's decision to move to the Rubio camp, first reported by Politico, comes as the party’s top figures grow increasingly alarmed by Donald Trump’s rise and looks for ways to stop his momentum.

Short has been highly respected for running Freedom Partners, the Kochs' political organization, for the past five years.

"Marc leaves behind a strong leadership team at Freedom Partners and working with them, we will continue to work to further our goal of a free and prosperous society for all Americans," Mark Holden, Freedom Partners' chairman of the board, said in a statement Tuesday. "We look forward to continuing our work with our partners to further these goals in 2016 and beyond."

Short's move is further evidence that Republican party leaders are uniting behind Rubio as the strongest alternative to Trump, who has won primaries in New Hampshire and South Carolina and is favored to win the Nevada caucus Tuesday.

Alex Conant, a spokesman for Rubio, confirmed Short will join the campaign but declined further comment.

Since his second-place showing in Saturday's South Carolina primary, Rubio has gained endorsements from 15 members of Congress and Gov. Asa Hutchison of Arkansas, which holds its primary March 1.