Donald Trump wasn't invited to address the retreat of some 450 top conservative donors who gathered here at a lush oceanfront hotel for a policy-focused retreat hosted by the Koch brothers and their powerful political network.

So the real estate magnate turned to Twitter on Sunday to mock rivals -- former Florida Gov. Jeb Bush, Florida Sen. Marco Rubio, Wisconsin Gov. Scott Walker, Texas Sen. Ted Cruz and former Hewlett Packard chief executive Carly Fiorina -- who were given entrée to potential backers at the luxurious gathering.

\"I wish good luck to all of the Republican candidates that traveled to California to beg for money etc. from the Koch Brothers,\" Trump tweeted Sunday. \"Puppets?\"

With that provocative two-pronged jab -- charging the billionaire industrialist brothers with attempting to buy influence, while attacking the integrity of the five candidates favored by the Kochs -- Trump may be asking for a fight. While the billionaire businessman likes to boast that he doesn't need anyone's money to fund his presidential ambitions, there are few independent organizations on the GOP side with political muscle to winnow the field -- and potentially knock Trump from his perch -- like the Koch-backed network.

The Koch's deep-pocketed political organization plans to spend $889 million by the end of 2016 to drive its free-market policy and philanthropic agenda, as well as direct electoral support to the candidates of its choosing.

Exactly how that money will be spent was part of the agenda here this weekend. And for the first time, some sessions at the private gathering were open to reporters, as long as they agreed not to identify donors without their permission. The attendees were not permitted to take electronic devices into the strategy sessions; cell phones were collected at the door.

Throughout the weekend, Koch network leaders briefed some 450 donors, who pledge six-figure sums to become members of the Freedom Partners organization, on their policy and philanthropic goals for the 2016 cycle.

Many of the discussions were heavy on policy issues. A Sunday afternoon session, for example, attended by several hundred attendees focused on legislation that would limit mandatory minimum sentencing, as well as other forms of criminal justice reform. At an evening reception, the featured speaker was Dr. Michael Lomax, president of the United Negro College Fund.

At this Koch network session and others this year, organizers said they will be seeking input from members to determine how the organization will spend its money and which candidates the Koch-funded groups will support in the 2016 cycle.

Even in an election cycle awash in cash, those resources could be pivotal. The Freedom Partners Action Fund, the super PAC tied to the Koch organization's umbrella group, plans to spend $100 million this election cycle.

Beyond the airwaves, the Koch-funded Americans for Prosperity has spent the last few election cycles mining voter data and building a grassroots army that could help steer voters in the direction of one or several presidential candidates favored by the Koch network.

Americans for Prosperity plans to spend at least $75 million this year continuing to build out those activities; and double that amount to $150 million next year.

Already the Koch network is giving the top five candidates identified by Charles Koch as the favorites -- Cruz, Walker, Rubio, Bush and Paul -- a platform to share their ideas at well-lighted, well-attended events in early primary states like New Hampshire, Iowa and Nevada.

Though the candidates could not explicitly ask for money at this weekend's gathering because it was hosted by the Freedom Partners non-profit, it gave them the chance for intimate chats about their policy goals and experience with potential backers.

The Koch brothers have indicated that they are unlikely to settle on one Republican candidate when they are looking at what they view as a strong field of candidates aligned with their policy goals.

In an interview with USA Today in April, Charles Koch said Bush, Rubio, Cruz, Paul and Walker were \"the ones we have talked to the most and who seem to be the possible leaders.\"

\"What we've told them all is that right now, we're not supporting anyone,\" Koch told USA Today. \"We're telling them that if they want our support, one way to get it is articulating a good message to help Americans get a better understand and a better appreciation of how certain policies will benefit them and will benefit all America.

At the top of that agenda, Koch told attendees this weekend, is convincing elected officials to phase out \"corporate welfare\" in the form of subsidies, regulations \"trapping people in poverty,\" as well as mandates and preferences for businesses \"that enrich the haves at the expense of the have nots.\"

\"This is an inspiring vision,\" Koch told the group, \"but to advance it, we must learn to be much more effective in articulating it and we must be true to it ourselves in our own activities and our own communities.\"

\"We talk here about dollars and raising money and they are absolutely critical to getting this done,\" Koch said. \"But they alone will not do the job. We know this from the successful movements in our country's history. It took the full commitment from the founding fathers, Frederick Douglass, Susan B. Anthony, Martin Luther King, Jr., and the thousands of others who led successful movements. To defy the odds stacked against them, these leaders had to pledge their lives, fortunes and their sacred honor -- often at great personal sacrifice.\"

\"That is the challenge before is. Will we rise to it? We're off to a good start,\" he said. \"I hope you will join me. Our country's future depends on it.\"

Though Democrats have spent tens of millions of dollars seeking to vilify the Kochs and their agenda -- portraying them as wealthy industrialists who have put the disadvantaged at risk to help their bottom line, the candidates who came here to woo donors this weekend did not show any hesitation in seeking their favor.

For the most part, they also ignored the needling by Donald Trump.

Walker, who was aided by Koch allied groups in his fight against big labor in Wisconsin, said Saturday that he wished \"the whole world could see what goes on here\" at the Koch network gatherings.

\"I point out, time and time again, so many of you here aren't here because of any interests on behalf of your personal finances or your industries, you're here because you love America,\" Walker said, comparing frustrations of some Koch network donors to those he has heard from tea party supporters. \"You care deeply about the future, you care about your children and your grandchildren, and I think David and Charles (Koch) have harnessed that frustration and said --- instead of just being angry about it, let's do something about it.\"

Bush, who received a very warm reception from Koch network donors during his session Sunday night, said he was honored to take part in the forum. He spoke freely about his plans for immigration reform and highlighted his record of cutting taxes in Florida.

Bush also unabashedly owned the characterization of him as the \"$120 million man\" -- a reference to the amount raised so far by his campaign and political action committees supporting his bid. \"How much is too much?\" he was asked.

\"You know, I don't know, but you might as well frontload it if you can,\" Bush said unapologetically to laughter. \"This is a long haul. Are we just supposed to say, 'Ok, let's just kind of warm up and work your way into it? Am I missing something here? I'm not running to come in third. I'm not running to, you know, have it on my resume that I ran for President.\"

The point of his effort, he said, \"is to run with purpose, run with heart, run in a way that draws people toward our cause -- and money helps,\" Bush said. \"I'm playing by the rules of the game the way it's laid out. And if people don't like it. That's just tough,\" he said.

All of the candidates dealt gingerly with Trump when asked to explain his position at the top of the polls in recent weeks. With Trump's appearance on the debate stage looming this week, Cruz used humor to diffuse a question about how Trump would play in the debate.

\"I have a lot of skills, but predicting Donald Trump is not one of them,\" Cruz said to laughter.

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