Sadly, there have been other times in the past when that was not true. As war raged for years in Europe during WWII, before the US entered the fray, there were supporters of the nazi regime and apologists for Hitler. It's pretty thoroughly documented in Bradley W. Hart’s book, Hitler’s American Friends: The Third Reich’s Supporters in the United States.

Hell, the US even turned away refugees – including denying entry to the family of Anne Frank.