When, on the campaign trail, Joe Biden compared his platform to the New Deal—and, by extension, himself to F.D.R.—who really believed him? Certainly not the left of his party. For a generation, the “end of big government” has been near-consensus in Washington, attested to even by Democrats such as Bill Clinton, as well as by Republicans who ran up gigantic deficits. In his hugely ambitious, multi-trillion-dollar plans, Biden argues for big government—very big government—as a force for positive change. Those plans may well fail to win the votes he needs in Congress, because the contemporary United States no longer resembles the country that embraced the New Deal. “You can’t put F.D.R. in Dr. Who’s phone booth and bring him to 2021 and he’ll address the American people,” the historian Jill Lepore says. David Remnick discusses the promise and challenges that Biden faces, with Lepore, Susan Glasser, Jelani Cobb, and John Cassidy.