Clues to their policy preferences can be found in their family foundation’s pattern of giving. For example, they have given more than once to groups questioning climate-change science. But their donations have flown to groups all over the conservative political map, ranging from libertarian organizations to movement conservative groups to the Koch brothers’ Freedom Partners Action Fund to Breitbart. That scattershot approach suggests the family has some ideological flexibility.

No one seems to know what motivates the Mercers or what policies they want to see enacted, even people who have worked closely with them or for projects funded by them. While they’ve poured money into conservative causes, they’ve also invested in projects explicitly aimed at overturning the modern conservative movement, like Breitbart News, in which they reportedly invested $10 million, and Trump himself. And the mystery of their ideological motivations is made all the more striking by their success in helping Trump reach the White House. A recent Wall Street Journal story on the Mercers concluded: "It isn’t clear what specific policies or positions, if any, the Mercers are seeking for their support of Mr. Trump."

“All I can take away is that they just want to be power players,” said a former Breitbart News staffer, who spoke on condition of anonymity because of a non-disclosure agreement. “I don’t know what their principles are. I don’t know how you switch from Ted Cruz to Donald Trump so quickly.”

“Most of these people I think I understand,” said a Republican operative who has been engaged on several Mercer-led efforts. (Like most people quoted in this story, the operative declined to be identified for fear of legal or professional consequences for speaking publicly about the Mercers.) “I don’t understand the Mercers.”

Rebekah Mercer “talks business. She talks data, she talks trends, she talks messaging,” said another Republican operative who has worked with the Mercers. “I have never really been in her presence where she’s talked policy.”

Asked to describe what’s motivating them, Bannon himself was vague.

“Really incredible folks,” Bannon said in an email. “Never ask for anything. Very middle class values as they came to their great wealth late in life.”

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Robert Mercer got his start at IBM, working there for over 20 years. He went to Renaissance Technologies in 1993. It’s there that Mercer, already well into middle age, became wealthy. Renaissance, based in East Setauket, Long Island, includes three hedge funds managing over $25 billion in assets, as well as the mysterious Medallion Fund, an employees-only fund that has made its investors unimaginably rich. Mercer’s co-CEO is Jim Simons, a major donor to Democrats; one Republican operative with connections to the Mercers who spoke on condition of anonymity joked that the pair were trying to “hedge the political system.”