In for a penny, in for a pound? Do perceptions of support parties shift with governing coalition partners?

Research has demonstrated that voters use a coalition heuristic in their perceptions of party policy shifts: Junior coalition partners are perceived to shift in parallel to Prime Minister parties. Several mechanisms account for this: (a) Voters recognize that coalition partners are pressured to compromise over policy, (b) parties of similar positions often form governing coalitions, (c) parties in coalition are less likely to differentiate themselves in public during the legislative term, (d) coalition parties work jointly though legislative and government institutions in policy-making and implementation. The role of ‘support’ parties has not yet been examined, and political scientists know little of how voters perceive these parties. All four mechanisms mentioned above should also apply to support parties even though they officially remain outside the formal coalition. Drawing on data from over 20 Eastern and Western European countries, we document to what extent the coalition heuristic applies to support parties, and whether voters perceive their shifts as similar to coalition partners in tracking the prime minister. Our results have important implications for electoral competition and government formation.