I don't know that this is a "new" phenomenon. This really goes back to the America-Firsters before WWII like Henry Ford, Father Coughlin, and Charles Lindbergh. There has always been a sleazy rathole of Jew-hatred in America thinly hidden under the veneer of nationalism.
What is allowing this vermin to be more open now is the meteoric rise in the public acceptability of anti-Zionist libels, as well as the worship of anti-Semitic, pro-Arab presidential candidate Barack Hussein Mohammed Osama.