In 2004 … die-hards in both parties felt that the choice between George W. Bush and John F. Kerry was much sharper on a host of issues than in any presidential contest going back to 1984. But when political scientist Marc J. Hetherington quizzed moderates, he found to his surprise that he got the opposite answer. … If anything, moderates in 2004 saw the Republican and Democratic nominees as being more alike than in any election since 1988. The schism between moderates and partisans has intensified in this election …
Hetherington believes that much of the loyalists’ perception of a yawning divide has little to do with issues. Rather, he said, what has happened in recent years is that partisans have come to identify with their parties in much the manner that sports fans identify with their teams. The strong views they feel on many issues do not drive their party affiliation; it is their party affiliation that drives their strong views.
"Let’s say you are a left-leaning person," Hetherington said. "You don’t really follow politics, but through the blogs you know the Democrats are here on the bailout and immigration and health care. All of a sudden, you know where you are supposed to be on these issues. It is not as though you really care about the bailout."
There is another piece of evidence that party identification rather than ideology is behind the growing polarization of the electorate: On a variety of unrelated issues — gun control, the economy, war, same-sex marriage, abortion, the environment, the financial bailout — the views of Republicans and Democrats have become increasingly monolithic. There is no reason someone who is against abortion should necessarily also be against gun control or for economic deregulation, but that is exactly what tends to happen among committed Republicans. Loyal Democrats have similarly monolithic views on unrelated issues.
"Party identification is part of your social identity, in the same way you relate to your religion or ethnic group or baseball team," said Gary C. Jacobson … This explains why, on a range of issues, partisans invariably feel their side can do nothing wrong and the other side can do nothing right. … Moderates … are like people who are uninterested in sports and roll their eyes when fans of opposing teams hurl abuse at each other.
Another consequence of intense party identification is that the Democratic and Republican parties have rid themselves of contrarians. Liberal Republicans and, to a lesser extent, conservative Democrats are endangered species. … In previous eras … these divisions were not primarily along party lines. The Vietnam War bitterly divided the country, for example, but the divide was hardly partisan. … Knowing whether a person is a Republican or a Democrat today tells you far more about their views on many issues than it did in previous eras.
One implication of this thesis is that it makes little difference what positions presidential candidates take on issues. People’s views — on the war, immigration or the economic bailout — come down largely to their party affiliation.
If you are a strong partisan, and if you accept the above as explaining where your strong correlated policy views come from, I beg you to reconsider: you just can’t reasonably be that confident your party is that consistently right on all those issues.