Studies of development and change in partisan fortunes in the US emphasize epochs of partisan stability, separated by critical events or turning points. Yet to date we have no estimates of legislative regimes as they relate to electoral realignments. In this paper we study partisan balances in the US Congress using the method of Markov switching. Our estimates for the House of Representatives are based on election changes from 1854, roughly the date of the establishment of the modern incarnation of the two-party system, to the present. For the Senate, we estimate partisan balance from 1914, the date of popular election of Senators.
We use this method to estimate an underlying unobserved state parameter, C+partisan regimeC-. Basically a partisan regime denotes a built-in congressional electoral advantage that persists through time, and that changes in a disjoint and episodic fashion. The method allows the direct estimation of critical transition points between Republican and Democratic partisan coalitions. Republican regimes characterized House elections during three periods: 1860 through 1872, 1894 through 1906, and 1918 through 1928. A three-state estimate for the House suggested the emergence of a third state in 1994. For the Senate, the two-state model does not fit adequately. We estimate a three-state model in which a Republican regime dominated from 1914 through 1928; a Democratic regime characterized the period 1930-1934, and a Democratic-leaning regime characterized the period 1938 to the present (1936 is a transition year). Combined with existing historical evidence, our analysis isolates four critical congressional elections: 1874; 1894; and 1930, and 1994.
