The most important fact about campaign contributions is barely anyone makes them. About one-half of one-percent of adult Americans gave more than $200 to a federal candidate in the 2011-2012 cycle. About four percent contributed if you look at donations under $200.
And there's huge inequality in these donations: the big donors matter much, much more than the small donors. The Sunlight Foundation calculates that "more than a quarter of the nearly $6 billion in contributions from identifiable sources in the last campaign cycle came from just 31,385 individuals, a number equal to one ten-thousandth of the U.S. population."
Think about all that when you look at this graph:
The chart comes from Ray LaRaja and Brian Schnaffer and it shows what most people intuitively know: the small minority of people who fund American politics are much, much more politically polarized than the vast majority of people who don't contribute to campaigns.
Which makes sense. You're a lot likelier to contribute to a political campaign if you think the fate of the nation rests of your guys defeating the other guys. You're a lot less likely to contribute to political campaigns if you don't much care which party wins.
But what happens next makes sense, too: politicians have to appeal to the people who fund their campaigns. The people who fund their campaigns really believe the other party is terrible. And so spending a lot of time working across the aisle or questioning your party's political strategy is not going to make your donors very happy.
