In his chapter on Party Polarisation, Brian Schaffner draws upon a range of research in order to examine the extent to which external and internal factors have caused the polarisation of Congress as identified by research drawing upon Poole and Rosenthal’s NOMINATE scoring. Such research found that legislative voting in both the House and the Senate has become increasingly split along party lines over the last four decades. Several explanations have been put forward to suggest why this may be the case, although, for the most part, each of these explanations is consistent one of two broader schools of thought on the issue.
The first of these is the belief that it is external (outside of the legislature) factors that have caused Congress to become so polarised. This view is consistent with the theories of David Mayhew (The Electoral Connection, 1974) who asserts that the desire for
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Thus, the belief that the polarisation of congress must have spawned from an increasingly divided electorate is too simplistic. Fiorina, Abrams and Pope (2006) alternately suggest that rather than ideological divisions increasing within the U.S. population, ideological consistency is increasing on a personal level for voters. This belief is supported by a decrease in split-ticket voting in congressional elections as constituents are now more likely consider their political views to be compatible with those of one specific party. In effect, this would cause conservative Democratic voters and liberal Republican voters to switch their allegiances, the likes of which did occur during the southern realignment that began in the