Senators representing their parties, not their states

Yesterday, I linked to Kombiz Lasvany's graph showing the difference between the percentage of Republican governors who signed a letter asking for state relief funds (70 percent) and the percentage of Republican congressmen who voted for those funds (about zero).

This got me interested in the degree to which members of Congress are representing their parties rather than their states. So I asked Dylan Matthews to work up two graphs testing this. The first shows how Democratic and Republican senators voted on the relief funding. As you can see, there was virtually no breaking of ranks. If you knew a senator's party, you could predict their vote almost perfectly:

Compare that with this graph grouping votes by unemployment rate. We separated the Senate into two categories: senators from states with less than 8.5 percent unemployment (which is the median state unemployment rate), and senators from states with more than 8.5 percent unemployment. As you can see, there's plenty of crossover. Knowing the unemployment rate of a state wouldn't be of much help in predicting a senator's vote:

Senators, in other words, are representing their parties, not their states. You see this particularly clearly when you look at states with one Republican and one Democratic senator. Kit Bond and Claire McCaskill represent the same state, with the same economic conditions, but they've been on the opposite side of most of these votes.