What is the main idea of this document?

Document 4: "Letter from Attorney General" (1942) Dear Grace, Please tell the President to keep his eye on the Japanese situation in California. It looks to me like it will explode any day now. There is tremendous public pressure to move all of them out of California - citizens and aliens - and no one seems to worry about how or to where. There are about 125,000 of them, and if it happens, it will be one of the great mass exoduses of history. It would probably require suspension of the writ of habeas corpus - and my estimate of the country's present feeling is that we would have another Supreme Court fight on our hands. James Rowe, Assistant to the Attorney General Context: "Habeas corpus" is the right to trial by jury if arrested for a crime. Suspending it would mean that the federal government could hold American citizens in prison without trial for an undefined period of time.