Marc Short, a top Koch Brothers operative, joins Marco Rubio’s campaign

The presidential campaign of Sen. Marco Rubio got a boost Tuesday when a top Koch Brothers operative joined the team, the latest move is a series indicating that the party establishment is coalescing around the Florida senator.

Former Oliver North aide Marc Short left a powerful job running the billion-dollar Freedom Partners donor network to join the Rubio campaign, friends confirmed.

The move comes as a major surprise to politics watchers, particularly because of its timing. It’s not clear whether it represents a move by the Kochs to back Mr. Rubio as the only viable alternative to tycoon Donald Trump or Sen. Ted Cruz, both of whom party leaders see as likelier to lose to the Democratic nominee in November.

“I have known Marc Short for many decades and have never known him to make a bad decision — or to put money over principle,” said Mr. North, a Fox News military commentator and a Reagan-era National Security Council staffer who helped aid the Nicaraguan anti-communist “Contra” rebels.

Charles and David Koch are among the wealthiest conservative businessmen with an interest in politics, but they have not settled on whether they will back any of the GOP presidential hopefuls.

Mr. Short did not respond to phone or email questions about why he left Freedom Partners or what he would do for the Rubio campaign.

For his part, Mr. Short has been involved for decades in conservative activities. He once ran Mr. North’s Freedom Alliance, a military charity best known for providing college scholarships for the children of U.S. service members killed in action.

Along with his wife, Kristen, Mr. Short also managed the Reagan Ranch in California for some years as part of the Young America’s Foundation.

On Tuesday, Mr. Rubio received another boost from outside, as a super PAC announced more than $3 million in ad purchases by next week in eight of the 10 “Super Tuesday” states, where political advertising has been light as attention has focused on the four earliest-voting states.

Conservative Solutions PAC is spending the biggest amount — in $1.4 million — in the megastate of Texas, the home state of Mr. Cruz.

One ad shown to reporters calls Mr. Trump “erratic, unreliable” and says Mr. Cruz is “calculated, underhanded.” The ad concludes: “Marco Rubio, the Republican who can beat Hillary and inspire a new generation.”