Scholars have long debated the strength of voters' partisan attachments, asking whether party identification plays a near-deterministic role in political decisions. A large literature argues that partisan cues dominate political choice, but other studies show that competing information can rival, and even sometimes outweigh, the effects of partisanship. We reconcile this conflicting evidence by theorizing that variation in the dominance of partisanship is due to the salience of the other considerations pitted against it. Using survey experiments that characterize the role of partisanship relative to both high and low salience issues, we demonstrate a pattern of ``Conditional Party Loyalty.'' Partisan dominance occurs when political choice is centered around issues with low public salience. However, partisans defect from co-partisan candidates if they disagree on enough high-salience 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.