It took a little while to realize that Sen. Elizabeth Warren was standing right in front of us. RootsCamp, the annual “unconference” that sequesters thousands of hopeful progressive activists in the Washington Convention Center, kicked off with an hour of punchy, concise speeches. Almost none of the press had arrived in the plenary ballroom when the freshman Massachusetts senator, the one they keep writing will-she-run-for-president tales about, got up for an unscheduled 9-minute address. “I wanted to be with people who get things done!” said Warren. No one had announced her name, and she didn’t give it—none of that was...