Three potential Republican presidential candidates appeared before a gathering of wealthy donors organized by the conservative billionaire Koch brothers in California on Sunday night.

The summit, held at a luxury resort near Palm Springs sealed off to outsiders, drew Republican Sens. Marco Rubio from Florida, Rand Paul from Kentucky and Ted Cruz from Texas.

It was organized by brothers Charles and David Koch, successful industrialists who bankroll conservative causes across America. Access to their network of money and influence is alluring to some potential Republican presidential hopefuls.