Voters often rely on partisan attachments as they evaluate new policy proposals, but does partisanship also color their interpretation of incumbent efforts to entrench themselves in power by changing the "basic rules of the political game"? We explore this question by taking advantage of a rare instance where a single party held a supermajority sufficient to unilaterally amend the constitution and overhaul the electoral system. We embedded a randomized experiment in a panel survey around the 2014 Hungarian elections, providing respondents with different information about recent changes to the Hungarian electoral rules. While respondents were largely pessimistic about the reforms, providing information yielded no significant effects on their views on the elections' legitimacy. But when information was presented alongside partisan cues, respondents became more negative in their views. Subgroup analysis shows that this effect is concentrated entirely among those not supporting the incumbent. Partisan differences in opinion dwarf any treatment effects we were able to induce. We provide evidence that these findings are unlikely the result of a well-informed populace. Rather, we provide the first experimental evidence that partisan-motivated reasoning applies not only to public policy under fixed institutions but also to changes to the institutional rules of a political system. Incumbents can exploit strong partisan attachments to reduce political competition.