This paper draws from the literatures on institutional design, constitutional separation of powers, judicial independence, and party system institutionalization to synthesize an integrated theory that explains why parties in legislature might transcend their own interparty competition and instead temporarily unite to wage interbranch conflict. Specifically, it seeks to determine the conditions under which a united legislative branch might empower a judicial branch as an ally in reining in an inordinately powerful executive branch. We then take an in-depth look at the case of Chile, where this very phenomenon occurred after the transition to democracy in the late 1980s and 1990s. In doing so, this paper seeks to contribute to the literature on judicial independence by explaining one motivation for strengthening it. It also builds on the literature on party system institutionalization, as only highly institutionalized party systems can muster the negotiating power to cooperate in achieving such an ambitious goal.
