WASHINGTON — The top political adviser in Washington to the Koch brothers will join Marco Rubio’s presidential campaign in another sign the GOP establishment is trying to bolster the Florida senator’s White House bid.

Marc Short, president of Freedom Partners, will become senior adviser to Rubio’s campaign.

Freedom Partners is the umbrella political organization of Charles and David Koch, the billionaire brothers who are among the most generous supporters of Republicans.

“This is a big get for Rubio,” Phil Cox, former executive director of the Republican Governors Association, told Politico.

“Marc brings a unique perspective as one of the few people who have had one foot in traditional Republican Party politics and another in more movement-conservative efforts.”

Rubio this week won endorsements from ex-Sen. Bob Dole and Rep. Peter King (R-LI).