ROBERT C. LIEBERMAN is Krieger-Eisenhower Professor of Political Science at Johns Hopkins. He has received fellowships from the Russell Sage Foundation and the American Philosophical Society. SUZANNE METTLER is the John L. Senior Professor of American Institutions in the Government Department at Cornell University. She is a recipient of a Guggenheim Fellowship and a Radcliffe Institute Fellowship, and was elected to the American Academy of Arts and Sciences in 2017.