Sen. Elizabeth Warren (D., Mass.) asked big Wall Street banks to disclose financial contributions to think tanks, a request that came several days after a centrist Democratic think tank blasted Ms. Warren’s “economic populism” on issues including Social Security.

The opinion piece in Monday’s Wall Street Journal by officials at think tank Third Way highlighted a battle among Democrats about the future direction of their party. After the piece ran, the Daily Kos, a liberal blog, noted the heavy presence of investment bankers on Third Way’s board. And the Progressive Change Campaign Committee created an online petition calling on Third Way to “publicly reveal its Wall Street donors so everyone knows why they are attacking Elizabeth Warren.”