Party identification is now a powerful indicator of how someone votes in national elections.

Excerpts from a 3-29-05 Washington Post article entitled:

Partisan Polarization Intensified in 2004 Election
Only 59 of the Nation's 435 Congressional Districts Split Their Vote for President and House

Political polarization intensified during the 2004 elections, continuing a trend that has defined voting behavior for most of the past decade and that has left the two major parties increasingly homogenized and partisan.

Only 59 of the 435 congressional districts went in different directions in presidential and House elections last year, according to newly released data from the political analysis firm Polidata. In the remaining districts, voters either backed both President Bush and the Republican House candidate or John F. Kerry and the Democratic House candidate.

In 2000, there were 86 such "split-ticket" districts, and in 1992 and 1996, there were more than 100 such districts.

The steady decline in districts where voters pick different parties to represent them in the White House and Congress reflects in part the effects of the redistricting process, which has created more and more strongly Republican or strongly Democratic districts.

In the presidential race, 93 percent of self-identified Republicans backed Bush and 89 percent of Democrats supported Kerry. Independents went 49 percent for Kerry and 48 percent for Bush.

In the more distant past, voters were far more likely to split their tickets when voting for Congress, particularly in the era when the South was heavily Democratic, albeit conservative. But the GOP takeover of the South, and to a lesser extent the decline of Republican moderates and liberals in the Northeast, has produced the new patterns.

[These] figures show again the depth of the Democrats' problems in the South. Not only did Bush carry every southern state, he carried the overwhelming percentage of congressional districts, except those where minorities are in the majority.

How would Bush and Kerry have fared if the electoral college determined its allocation of electoral votes on the basis of who won each congressional district, as some advocate, rather than on who wins the popular vote in each state? Bush would have won by an even larger margin, with 317 electoral votes rather than the 286 he actually captured.