Do partisan disagreements over politically-relevant facts, and preferences for the information sources from which to obtain them, represent genuine differences of opinion or insincere cheerleading? The answer to this question is crucial for understanding the scope of partisan polarization. We test between these alternatives with experiments that offer incentives for correct survey responses and allow respondents to search for information before answering each question. We find that partisan cheerleading inflates divides in factual information, but only modestly. Incentives have no impact on partisan divides in information search; these divides are no different from those that occur outside the survey context when we examine web browsing data from the same respondents. Overall, our findings support the motivated reasoning interpretation of misinformation; partisans seek out information with congenial slant and sincerely adopt inaccurate beliefs that cast their party in a favorable light.