It's hard to pick the most outrageous act of the Franklin D. Roosevelt administration, but a leading candidate has to be Executive Order 9066. This deprived over 110,000 people legally living in the United States, some 70,000 of whom were American citizens, of their freedom solely because of their ancestry.
Eric Muller's American Inquisition doesn't tell the whole story, and it covers only a small part of Roosevelt's villainy. It deals specifically with the procedures for establishing the loyalty or disloyalty of Issei (Japanese-born) and Nisei (native-born citizens with Japanese parents) after they were placed in concentration camps.
Several different government agencies competed for dominance in deciding Japanese-Americans' fate, creating an atmosphere in which the rules kept changing. Arbitrary checklists made childhood trips to Japan, studying or teaching Japanese, or being a Buddhist evidence of "disloyalty." The greatest proof of treasonous intent was acting like an American and objecting to one's treatment.
In 1944 the government's actions came under a serious legal challenge, which went to the Supreme Court. The administration's response was to delay as much as possible, at least till after the election. In November, after Roosevelt had won his fourth term and picked up four House seats in California, and just as an unfavorable ruling from the Supreme Court was imminent, Roosevelt agreed to end the mass exclusion of Japanese-Americans. About 10,000 people (a politically selected number) remained excluded on a nominally individual but capricious basis. Roosevelt continued to push for scattering them around the country, separating them from each other and from their communities.
Muller argued that the loyalty tests were largely based on racial theories. The Japanese were seen as an "enemy race" whose brains didn't work the same way as Americans'; family loyalty, not personal views, determined the actions they would take.
The attempt to weed out people based on loyalty rather than concrete actions was a mistake at its root, as Muller notes:
Loyalty is too ephemeral and ambiguous a criterion to support a national security program, especially in a racially or ethnically charged setting. When government officials on a loyalty inquest screen citizens for hidden biases and motivations, they are likeliest to find their own.
American Inquisition isn't a suitable introduction to Japanese-American relocation in World War II; it leaves out nearly all of the broader context. But it's too little remembered that the liberal Roosevelt administration treated a large group of Americans in a much worse way than anything the Bush administration is doing to Muslims today. This book helps to keep the fact in our memories.