After the Buffalo shooting there seemed to be more people noticing and questioning why it was always totally sympathetic, unthreatening soft-targets that were being shot up. No one was shooting up a Fortune500 company hq or a high-end country club or some bar association meeting or a banker's wedding. More people were finding it statistically improbable that the disaffected very rarely attack "the system" itself.
...and then some nut, who seems to have done everything possible beforehand to get caught, goes after Kavanaugh. One of the system's very own gatekeepers. Someone much of the country, certainly the media, isn't naturally sympathetic towards.
When the anarchists that were coming into the country from Europe in the waves of immigration in the late 19th Century and early 20th Century started targeting the elites, the result was the Immigration Act of 1921 and then 1924, which cut it off.