he belief that ideologically disparate senators must have different support coalitions or constituencies within a state is sõ~-widespread that many scholars take it to be virtually axiomatic ; their inquiries deal only with uncovering the coalitions or constituencies that must be molding the behavior of each senator. Bullock and Brady (1983) uncover those different support coalitions in different geographic constituencies in heterogeneous states. Poole and Rosenthal (1984) uncover them in ideologically extreme groups in all states. And Wright (1989) uncovers them in ideologically different party elites. Krassa and Davison (1988) also assume that ideologically disparate senators mobilize distinct reelection constituencies, but they find that those senators broaden their bases of support by papering over the full extent of their ideological disparity, especially in reelection years.The belief that ideologically disparate senators must have different support coalitions is deduced from the basic assumption that senators' ideological positions must reflect the wishes of the coalitions that put those senators into office: if senators take markedly different ideological positions, they must have had different support coalitions. That syllogism is explicitly stated in Poole and Rosenthal (1984: 1062), Krassa and Davison (1988: 2), and Wright (1989: 465). The major premise is a widely accepted assumption of political and economic research on elections and representation (see, e.g., Pitkin 1967; Peltzman 1984;Erikson and Wright 1985;Hamilton 1987).