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If Democrats go left, donors may get in the way.

According to a new Demos report, both major political parties draw from a mostly white, mostly male donor classand those donors tend to be more conservative than voters overall. Among the key findings from Whose Voice, Whose Choice:

While three-quarters of the adult population is white, and about 63 percent of the total population is white, 91 percent of federal election donors in 2012 and 92 percent of donors in 2014 were white. Among donors giving more than $5,000, 94 percent were white in 2014 and 93 percent were white in 2012.

• Men make up slightly less than half of the population, but comprise 63 percent of federal election donors. The pool of donors who give more than $1,000 has less gender diversity, with men making up 65 percent of donors giving more than $5,000.

• White men represent 35 percent of the adult population, but comprise 45 percent of federal election donors and account for 57 percent of money contributed.

Democratic donors are ideologically closer to the party’s voter base than Republican donors are to theirs. But when Democratic donors did diverge from voters, the results frequently undercut progressive policy initiatives. They mostly fought Obama’s push to expand SCHIP, his stimulus plan, and the Affordable Care Act. White male donors overall were more conservative than women donors on reproductive justice and specific policy issues like the Hyde Amendment. And the wealthier the donor, the more conservative they were likely to be.

These trends offer a partial explanation for the Democratic Party’s reluctance to take on a more progressive policy platform: It’s still beholden to the whims of a few exorbitantly wealthy white men. And that’s a significant obstacle to the party’s populist wing.