While partisan cues tend to dominate political choice, prior work shows that competing information can mute the effects of partisanship if it relates to salient political issues. But what are the limits of partisan loyalty? How much electoral leeway do co-partisan candidates have to deviate from the party line on important issues? We answer this question using conjoint survey experiments that characterize the role of partisanship relative to issues. We demonstrate a pattern of conditional party loyalty. Partisanship dominates electoral choice when elections center on low-salience issues. But while partisan loyalty is strong, it is finite: voters are more likely than not to vote for the co-partisan candidate until that candidate takes dissonant stances on four or more salient issues. These findings illuminate when and why partisanship fails to dominate political choice. They also suggest that, on many issues, public opinion minimally constrains politicians.