DANA POINT, Calif. (AP) — Billionaire industrialist Charles Koch warned America is "done for" if the conservative donors and politicians he gathered at a retreat this weekend don't rally others to their cause of demanding a smaller, less-intrusive government.

"History demonstrates that when the American people get motivated by an issue of justice, that they believe is just, extraordinary things can be accomplished," he said on Sunday, going on to reference the American Revolution, abolition of slavery and women's and civil rights movements. "We, too, are seeking to right injustices that are holding our country back."

Listening intently inside a tightly guarded luxury resort in Southern California were 450 business leaders — many among them top political contributors — and the elected officials who receive that largesse. They've been strategizing with officials at the education, policy and activist groups that Koch and his brother David have spent years building up and funding.

That network has a budget of $889 million through the end of 2016 — and much of it will be directed at electing a Republican to the White House.

As such, five GOP contenders are speaking to the donor group, answering questions. Florida Sen. Marco Rubio, responding to a question about why celebrity businessman Donald Trump is surging in GOP presidential polls, echoed Koch's sentiments that the country is at a crossroads.

"Americans instinctively understand that we have reached another one of those pivotal moments in our history where what's at stake is not what party is in charge but our identity as a nation and as a people," Rubio said. "And they want to see candidates that are passionate about that and will do something about it."

Trump wasn't as generous in his assessment of Rubio and the others who came to the Koch retreat, writing on Twitter: "I wish good luck to all of the Republican candidates that traveled to California to beg for money etc. from the Koch Brothers. Puppets?"

Former Florida Gov. Jeb Bush and Texas Sen. Ted Cruz are due to speak Sunday evening. Wisconsin Gov. Scott Walker and former technology executive Carly Fiorina took questions on Saturday.

Walker heaped praise on the donor crowd and said their patriotism reminded him of what he saw at tea party rallies, who may not have the net worth but who are also "fighting for their country.

"I wish the whole world could see what goes on here," Walker said of the donor conference.

The Koch donor conferences, held twice a year, are insular affairs.

Only those who have donated $100,000 or more to Koch-backed groups are invited. Yet even those deep-pocketed donors must check their mobile phones at the doors of some strategy sessions.

For the first time, a small number of reporters were invited to hear the 2016 candidates and attend some other forums. As a condition of attending, reporters were not permitted to identify any of the donors in attendance.

Most of the Koch-backed entities are nonprofits that do not have to disclose their donors. The two most politically active groups are American for Prosperity, which deploys activists to knock on doors and discuss issues important to the Kochs, and Freedom Partners, which has a super PAC that can spend directly on elections.

Although leaders for those two groups say they aren't endorsing anyone in the GOP primary, donors at the retreat have the ability to write million-dollar checks to boost a candidate's chances.

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