Los Angeles (CNN) There are few endorsements in the 2016 presidential race that could have as much impact as that of the Koch Brothers with their expansive political network, their state of the art voter data and ability to flood the airwaves to help their chosen candidate -- or candidates.

So there are few events as important to the top tier of GOP candidates as this weekend's oceanside retreat with Charles and David Koch -- and the many donors who have helped build their sprawling political network.

Notably not on the list of invitees to the Orange County city of Dana Point: billionaire Donald Trump, who has startled the political establishment with his strength in national and early state polls.

Who made the cut? Not Trump.

Only those who "we feel are great policy leaders at the federal, state and local level" were invited, said James Davis, a spokesman for Freedom Partners, the non-profit umbrella group presiding over the Koch's political empire

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