Adam Berinsky writes at YouGov that people who distrust the government are more likely to accept rumors about a politician or political group.
This graph plots the relationship between a person's confidence in the U.S. Department of Health's schedule of vaccines and the belief Obama was born in the U.S.
As confidence in vaccines decreases, belief that Obama was born in the United States decreases as well.
What is especially striking is the fact that the relationship holds among both Democrats (the blue line) and Republicans (the red line). There is, not surprisingly, a large difference in the average support for the belief that Obama was born in the United States among partisans of different stripes. However, both Democrats and Republicans who are less confident in the vaccine schedule are less likely to believe that Obama was born in the U.S.
In sum, Birtherism is not simply a condition of the Republican party; conspiratorial beliefs underlie expressions of misinformation from across the ideological spectrum.