Compromise or differentiate? The role of partner popularity in coalition parties’ strategic parliamentary speech

In coalition governments, while parties need to compromise with their partners to govern together, they also need to differentiate from the partners to please their supporters. How do coalition parties reconcile compromises with differentiation? We argue that coalition parties, especially junior partners, adjust their strategies to compromise or differentiate themselves from their partners depending on the level of public support for their partners. Parties tend to differentiate from partners when partners receive lower public support, and compromise with partners when they enjoy higher public support. To test this argument, we analyzed parliamentary speeches by legislators from a junior coalition partner in Japan. We applied a dynamic linear model to the results of machine learning text classification of legislators’ speeches. Our results show that as the senior party’s public support rate falls, the speech styles of legislators from the junior partner increasingly diverge from those of the senior partner’s legislators.