Sen. Elizabeth Warren called Wednesday for Democrats to adopt a muscular form of liberalism in a speech that included thinly veiled jabs at Bill and Hillary Clinton as examples of economic stewardship gone wrong.

Ms. Warren repeated assertions in a speech to an enthusiastic labor audience in Washington that the U.S. political system is “rigged’’ in favor of wealthy corporations at the expense of everyday families, an argument that has made her a darling of the left and the subject of efforts to draft her as a presidential...