It's no secret that billionaire brothers Charles G. and David H. Koch, arguably two of the United States's most influential big-money donors in conservative politics, have kept quiet this presidential cycle.

In the past the brothers have thrown hundreds of millions of dollars in the race for the White House through their extensive network of conservative anonymous donors and businesses. They unveiled a budget of up to $900 million for the 2016 presidential election cycle at their donors' retreat in January.

Now Charles Koch has floated the idea of endorsing Democratic frontrunner Hillary Clinton for president.

In an interview on ABC's This Week, Koch said, "it's possible" that a Clinton presidency would be better than anyone currently in the Republican nomination race, noting that former president Bill Clinton was "in many ways" a better leader than George W. Bush.

Koch's comments weren't a full vote of support, however. But he questioned whether she really means what she's been saying: "We would have to believe her actions would be quite different than her rhetoric. Let me put it that way," Koch said on ABC.

Unsurprisingly, Hillary Clinton says she isn't interested in their endorsement:

Not interested in endorsements from people who deny climate science and try to make it harder for people to vote. https://t.co/TWN4zYhMBh — Hillary Clinton (@HillaryClinton) April 24, 2016

A kind word from Koch probably won't help Clinton with critics who say she's too conservative for the Democratic ticket, as she's found it more difficult than expected to contend with the progressive ideals of Bernie Sanders. As a result, in the past months, Clinton has shifted some positions to the left, including endorsing the $15 federal minimum wage during the Democratic debate in New York.

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