Gary Younge nails it:

Where the right is concerned the marginal and the mainstream have rapidly become blurred. Neither the Tea Party nor Obama created these divisions. But over the past two years they have intensified to an alarming degree. Polls last year revealed that a majority of Republicans believe Obama is a Muslim and a socialist who "wants to turn over the sovereignty of the United States to a one-world government" while two-thirds of Republicans either believe or are not sure that the president is "a racist who hates white people", and more than half believe or are not sure that "he was not born in the US" and that he "wants the terrorists to win".