TPM and Think Progress have more debunking Bachmann's fear mongering.

Bachmann: Take this into consideration. If we look at American history, between 1942 and 1947, the data that was collected by the census bureau was handed over to the FBI and other organizations, at the request of President Roosevelt, and that’s how the Japanese were rounded up and put into the internment camps. I’m not saying that’s what the Administration is planning to do. But I am saying that private, personal information that was given to the census bureau in the 1940s was used against Americans to round them up and put the Japanese in internment camps.