How important are political parties in motivating and disciplining elected officials? Using a difference-in-differences design, we study how shocks to incumbents’ reelection probabilities affect legislative behavior in a setting where parties fully control candidate selection. We find that within-term variation in lame-duck status has a strong negative effect on legislative effort. There is, however, no clear evidence that lame-duck status affects the extent to which legislators deviate from the party line. Our findings align well with the citizen–candidate framework, where candidates have fixed ideological positions that do not vary based on electoral incentives.