Research on chief justices (CJs) has underscored the individual features of justices and the institutional characteristics of the office. We focus on an additional organizational dimension, the relationship between the CJ and the judiciary, arguing that it can become critical in periods of constitutional stress. We argue that insider CJs, those who reach the Supreme Court after a long career within the judiciary, have resources that outsiders lack: the backing of the corporation and judiciary’s esprit de corps as an important organizational source of strength and will to defend judicial autonomy as well as to serve as a check in contexts of constitutional tension. We illustrate the argument in the case of Mexico’s CJs during the administration of President López Obrador (2018–24), contrasting the tenures of outsider CJ Zaldívar and insider CJ Piña. We show that judicial corporatism in Mexico’s hyper-pyramidal judiciary has two edges, one that makes the judiciary inertial and sluggish and a brighter side that favors resistance to political takeover.