Party label does not always determine how a member of Congress will vote on a controversial hot-button issue, but when the party line is breached there is usually a compelling reason. While there can be myriad reasons a legislator votes one way or another, there is a strong correlation between lawmakers who vote against the party line on a divisive issue and the partisanship of the state or district they represent. (State or district partisanship is determined, for our purposes, by the share of votes won by a party"s presidential nominee. A state like Alabama, for example, has a 61.6% Republican state partisanship because that is the percentage won by President Bush in 2004.)
The recent cloture vote in the Senate on the immigration bill is a case in point. The bill was generally favored by Democrats and generally opposed by Republicans, by about 2 to 1 on either side. With such a contentious issue, one might expect party members to close ranks and try to "win one for the team."� With the immigration bill, however, there were significant "defections"� on both sides of the aisle. For Democrats, the "nay" votes strongly match up with the partisan makeup of the states that put them in office.
Here is a list of Democratic senators who "defected"� to vote against cloture, followed by the Republican partisan makeup of their respective states.
Baucus - MT - 59% R
Bayh - IN - 59% R
Bingman - NM - 49% R
Brown - OH - 50% R
Byrd - WV - 55% R
Dorgan - ND - 63% R
Harkin - IA - 56% R
Landrieu - LA - 56% R
McCaskill - MO - 52% R
Nelson - NE - 65% R
Pryor - AR - 54% R
Rockefeller - WV - 55% R
Stabenow - MI - 47% R
Tester - MT - 59% R
Webb - VA - 53% R
As you can see, in all cases but two, they hail from states with a majority Republican electorate. Although President Bush just barely edged out a win in Ohio, even Democrat Sherrod Brown voted in line with his state"s 2004 presidential choice.
For many Republicans, support of the bill is about as likely to be based on loyalty to the President as it is to correlate with the partisanship of their respective states, so the methodology used to understand the Democratic defections does not work as well. Democrats do not have the extra burden of appeasing a president, which makes the effect of their state"s partisanship all the sharper.
We can see this phenomenon in effect within other wedge issues that tend to divide the Democratic caucus in the Senate. On the vote for the 2005 flag burning amendment, nine of the twelve Democratic senators who voted for the amendment were from Republican-leaning states. All Democrats who voted to confirm Samuel Alito to the Supreme Court were red state dwellers.
The GOP is not totally immune, either (if somewhat more resistant). In the 2005 battle over the gay marriage ban, all the Republicans voting against the measure, save Arizona"s John McCain, were from Northeastern Kerry-voting states, as were all three of the Republicans who voted against extending Bush"s tax cuts in 2006. Of course, all defecting Democrats on these bills were from states that voted for Bush in 2004.
Check out our "Monopoly Politics"� reports to find out more about how district partisanship is one of the major factors we use to predict congressional elections, and keep coming back to FairVote.org as your best source for information on voting and electoral reform.