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Former President Obama has reportedly been vouching for Sen. Elizabeth Warren (D-Mass.) to wealthy donors in an attempt to "rally the troops."

Obama, The Hill reports, has in recent months "gone to bat" for the Democratic presidential candidate to "donors reluctant to support her given her knocks on Wall Street and the wealthy," describing her behind the scenes as a capable contender and encouraging them to support her if she's the nominee.

"He obviously thinks she's very smart," a Democratic donor said. "He thinks her policy ideas matter. And I think he sees her running the campaign with the most depth."

Obama has not offered any 2020 endorsement and has made clear he'll stay out of the Democratic primary. Still, the Hill reports that those around Obama say he's concerned Democrats in financial services will, per one ally, "have an issue" with Warren as the nominee, hence his attempt to "rally the troops." One Obama source noted, however, he would do the same for any one of the 2020 Democrats.

This comes after a report that Obama in 2015 said that if voters rallied behind Warren, who helped set up the Consumer Financial Protection Bureau in his administration, it would be a "repudiation" of his economic policies. It also comes after a September report on the "far more combative relationship" between Warren and the Obama administration "than she usually discusses on the campaign trail."