They build a fence around the capital to protect against them.
Since there's no way there are actual 1.9 million terrorists in the US. 1.9 million/326 million is about 1 person out of 200 on that list.
In all likely hood, its just a list composed of people in opposition to government.
Can't be many BLM protestors, and leftists, since government is flying their flags. Simple deductive reasoning will get you to that this list is mostly Trump supporters from his populist movement.
Just read the latest Terrorism Threat bulletin from DHS. Then visit Gab.com, if you have any doubts on the overlap.
Summary of Terrorism Threat to the U.S. Homeland
https://www.dhs.gov/ntas/advisory/national-terrorism-advisor...