Howell has written widely on separation-of-powers issues and American political institutions, especially the presidency. He currently is working on research projects on separation of powers issues, the origins of political authority, and the normative foundations of executive power.

Howell’s most recent book (with Terry Moe) is Presidents, Populism, and the Crisis of Democracy (University of Chicago, 2020). His research also has appeared in numerous professional journals and edited volumes.