This was written in 1931, as a part of an attempt to understand the previous decade:

Immigration was restricted, being put upon a quota basis, to the satisfaction of labor and the relief of those who felt that the amount of melting being done in the melting-pot was disappointingly small. Only Yesterday, By Frederick Lewis Allen, Ch. 6 Harding and the Scandals.

In the same book, (under the heading of THE BIG RED SCARE) you can read about some of the bombings directed against an immigrant restrictionist Senator , the Immigration Commissioner, and other government officials, apparently by foreign anarchists who didn't approve.