Unprecedented numbers of negative political advertisements aired in battleground markets during the 2012 primaries, the first presidential campaign since the 2010 Citizens United decision. Grounded in theories of involvement, this investigation parses the influence of partisanship and political expression on the affective effects of negative Super PAC ads. Based on a pretest–posttest design with two experimental conditions and 585 participants, the results indicate both enduring and situational involvement exerted significant main and interaction effects on viewers’ affect toward the general election candidates and the political parties. Driven by Independents who did not engage in political expression, these Super PAC ads evoked significant net decreases in affect toward Mitt Romney and the Republican Party and net increases toward Barack Obama and the Democratic Party. These results suggest enduring and situational involvement moderate the affective effects of negative Super PAC advertising in primary contests.