24 RUCHO v. COMMON CAUSE Opinion of the Court party’s advantage may be shown through sensitivity testing: probing how a plan would perform under other plausible electoral conditions.” Brief for Appellees League of Women Voters of North Carolina et al. in No. 18–422, p. 55. See also 318 F. Supp. 3d, at 885. Experience proves that accurately predicting electoral outcomes is not so simple, either because the plans are based on flawed assumptions about voter preferences and behavior or because demographics and priorities change over time. In our two leading partisan gerrymandering cases themselves, the predictions of durability proved to be dramatically wrong. In 1981, Republicans controlled both houses of the Indiana Legislature as well as the governorship. Democrats challenged the state legislature districting map enacted by the Republicans. This Court in Bandemer rejected that challenge, and just months later the Democrats increased their share of House seats in the 1986 elections. Two years later the House was split 50–50 between Democrats and Republicans, and the Democrats took control of the chamber in 1990. Democrats also challenged the Pennsylvania congressional districting plan at issue in Vieth. Two years after that challenge failed, they gained four seats in the delegation, going from a 12–7 minority to an 11–8 majority. At the next election, they flipped another Republican seat. Even the most sophisticated districting maps cannot reliably account for some of the reasons voters prefer one candidate over another, or why their preferences may change. Voters elect individual candidates in individual districts, and their selections depend on the issues that matter to them, the quality of the candidates, the tone of the candidates’ campaigns, the performance of an incumbent, national events or local issues that drive voter turnout, and other considerations. Many voters split their tickets. Others never register with a political party, and vote for candidates from both major parties at different