The senator, who as a congressman represented parts of the district, becomes the latest establishment Democrat to back Jeffries, who was recently invited to have his picture taken with President Obama. Obama does not endorse in open-seat primaries but the meeting sent a clear signal who he's behind.

The two are running to replace Rep. Edolphus Towns (D-N.Y.), who is backing Barron. Other Barron supporters include the AFSCME union's powerful local affiliate.