INDIAN WELLS, California — Most of the 500 wealthy conservatives gathered at a Southern California retreat this week know they want to see a Republican back in the White House, but many don't know what to do with the billionaire who wants to "make America great again."

Republican presidential front-runner Donald Trump was not at the biannual Charles and David Koch-organized conference over the weekend, but he was a constant presence on the minds of many here at the seminar hosted by the billionaire executives known for their active role in Republican politics.

"We had a bet — I think I'm losing right now — how far we could go before the name of the Republican front-runner was mentioned," said Sen. Ben Sasse of Nebraska, a Trump critic who participated in a panel discussion at the opening dinner Saturday evening.

The Koch network is unlikely to endorse a Republican presidential candidate in the primary, but what is less clear is if the conservative activists who spent $400 million in the last presidential election will actively try to defeat Trump in the primary. It's possible that they will and it's a decision that will be made after the early primary states have voted, a senior official at the Koch-backed political action committee Freedom Partners Action Fund told NBC News.

This was only the second seminar that has allowed reporters. A small number of journalists were invited to cover the event. Six news organizations, including NBC News, accepted in exchange for following some guidelines that included preserving participants' identity. Attendees were able to speak to the press if they chose.