This article tests two models of extremism versus moderation in presidential policy stances, a party activist theory and a congressional context theory. The party activist theory argues that, due to the electoral and nomination reforms of the mid-1970s, party activists became increasingly important and powerful in their parties. As activists tend to be more policy extreme than rank-and-file voters, and grew more extreme over the past several decades, this theory predicts presidents will also be more policy extreme in the postreform than the prereform era. The congressional context theory focuses on divided government and polarization. It argues that policy-minded presidents must moderate their policy positions during divided government because they need support from the opposition party. However, polarization erects barriers and disincentives for presidential moderation, offsetting the moderating tendencies of divided government. Using data on presidential policy positions from the 1950s through the early 2000s, I test both theories, finding support for the congressional context but not the party activist theory.