Democratic Party leaders and grass roots activists alike are at a loss to explain how the onetime champion of the 99 percent could cash in with a September address at a health care conference run by investment firm Cantor Fitzgerald.

"Spiritual leader of the people's #Resistance cashes in with $400k speech to Wall Street bankers," read one tweet.

"Obama's $400,000 Wall Street speech will cost @TheDemocrats much more than that," read another. "It reinforces everything progressives hate about Democrats."

Sen. Elizabeth Warren, D-Mass., said she "was troubled by that," when asked her opinion on Sirius XM's "Alter Family Politics" radio show this morning. But she held back from criticizing the president directly while referring repeatedly to her new book, "This Fight is Our Fight," in which she outlines her concerns about big money's influence on American politics.