On Tuesday, Sen. Bernie Sanders (I-VT), the socialist Senator who is considering challenging Hillary Clinton in the primary, called her out for not revealing what she stands for.

“Why don’t you tell me what Hillary Clinton is campaigning on,” Sanders said to MSNBC host Thomas Roberts. “Do you know? You don’t know and I don’t know and the American people don’t know.”

Sanders said the most important issue in the 2016 election is taking “on the billionaire class which has so much power over our economic and political life” and emphasized that he “can’t comment on Secretary Clinton until we know what she’s saying.”

Clinton has even frustrated her own supporters with her lack of specifics. Her website still is devoid of an issues section. Already, the Economist has asked on its cover, “What does Hillary stand for?” And the Washington Post has asked, “Why does Hillary Rodham Clinton want to be president?”

The three Republicans who have formally declared their candidacies–Sens. Ted Cruz (R-TX), Rand Paul (R-KY), and Marco Rubio (R-FL)–all have robust issues sections on their respective websites.