one hundred percent American

plural one hundred percent Americans

1. datedpolitically incorrectAn American who is white, native-born, and Protestant.

   1 more example

   On the other hand, a man with the external earmarks of the old American stock is accepted uncritically as a one hundred percent American. […] For the average Klansman, apparently, one hundred percent Americanism is often identified with the crude and unreasoned emotional enthusiasms that are excited by external symbols such as the flag, the soldier's uniform, or the words of the Declaration of Independence.

   1972, Myron A. Marty, Retracing Our Steps: Studies in Documents from the American Past, Canfield Press, →ISBN, page 211