Why is voting behaviour tied to ethnicity in many new democracies? A predominant view, offered by the instrumentalist theory, argues that voters use candidates’ identity -ethnic or partisan- as a signal of expected performance. However, voters will reward well-performing politicians by being more likely to vote for them and punish bad performance regardless of candidates’ identity. To test these assumptions, we conduct a nationally representative survey in Kenya asking voters about their spending preference for the country’s main anti-poverty programme, which is managed by MPs in collaboration with citizens. We find that voters, regardless of ethnicity or party, have an erroneous view of how their MP spent the anti-poverty funds. Then in an experiment, we share with voters the spending made by the MPs and audit results probing for corruption. Once voters are aware that their MP’s spending does not match their spending priorities, their approval and likelihood of voting for the MP decreases if primed to view the politician as partisan. Voters also electorally punish MPs for corruption whether copartisan or non-copartisan. In contrast to instrumentalist expectations, if voters are primed to view their MP in ethnic terms, they are more likely to vote for their coethnic overlooking bad performance and corruption. The availability of alternative parties in local elections may explain why voters attach partisanship to performance evaluation. Still, in our case study, as in other new democracies, politicians continue mobilising support along ethnic lines, perhaps explaining why voters prioritise group loyalties if primed to think about ethnicity.