Studies have observed that readers are more likely to trustnews sources that align with their own political leanings. We ask: is the higher reported trust in politically alignednews sources due to perceived institutional trustworthinessor does it merely reflect a preference for the political claimsaligned sources publish? Furthermore, do respondents re-port their actual beliefs about news or do they choose toexpress their political commitments instead? We conducteda US-based experiment (N=400) using random association ofnews claims to news sources as well as financial incentivesto robustly identify the main drivers of trust in news and toevaluate response bias. We observe a comparatively weakeffect of source on news evaluation and find that response dif-ferences are largely due to the alignment of the respondents’politics and the news claim. We also find significant evidencefor expressive responding, in particular among right-leaningparticipants.