Strengthening mainstream consensus? The effect of radical right populist parties on the defense policies of left parties

We study how the electoral success of radical right populist parties (RRPPs) affects mainstream parties' defense policy positions. The success of RRPPs threatens the credibility of established left-wing parties with coalition and international partners due to substantive overlap between their and RRPPs' defense-skeptical position. We argue that left parties adopt more assertive defense positions to distinguish themselves from RRPPs, thus increasing mainstream consensus on defense policy. Examining 27 European countries between the end of the Cold War and Russia's occupation of Crimea (1990–2013), we test this argument based on a regression discontinuity design around electoral thresholds for obtaining parliamentary seats. We find that, in response to RRPP success, left parties adopt more assertive defense policy positions, whereas center-right parties stand their ground. This study yields evidence for an adversarial response to the radical right, often thought to have lost out to accommodation, and for mechanisms other than electoral incentives, in a highly consequential domain.