Abstract: “Partyism” is a form of hostility and prejudice that operates across political lines. For example, some Republicans have an immediate aversive reaction to Democrats, and some Democrats have the same aversive reaction to Republicans, so much so that they would discriminate against them in hiring or promotion decisions, or in imposing punishment. If elected officials suffer from partyism – perhaps because their constituents do – they will devalue proposals from the opposing party and refuse to enter into agreements with its members, even if their independent assessment, freed from partyism, would be favorably disposed toward those proposals or agreements. In the United States, partyism has been rapidly growing, and it is quite pronounced – in some ways, more so than racism. It also has a series of adverse effects on governance itself, above all by making it difficult to enact desirable legislation and thus disrupting the system of separation of powers. Under circumstances of severe partyism, relatively broad delegations of authority to the executive branch, and a suitably receptive approach to the Chevron principle, have considerable appeal as ways of allowing significant social problems to be addressed. This conclusion bears on both domestic issues and foreign affairs.