After a slow start, she’s gaining momentum by pushing her party to embrace bold, left-wing ideas that could win back the Oval Office—or cost Democrats everything. Last fall, Elizabeth Warren got an email from Klaus Schwab, founder of the World Economic Forum, inviting her to speak at the group’s annual meeting in Davos in late January. He was taken with Warren’s sweeping moral critique of winner-take-all capitalism and looking to jolt the heads of state and global financial titans at his glittering conference in the Swiss Alps. Would she come to Davos and address them?