Anyone on a terror watchlist who tries to buy a gun should be thoroughly investigated by the FBI and the sale delayed while the investigation is ongoing. If an investigation uncovers evidence of terrorist activity or involvement, the government should be allowed to immediately go to court, block the sale, and arrest the terrorist.
The fascists do not want to go to court and arrest...because then they would have to PROVE their case. They would instead desire to just put a name on a list and ban someone from exercising their second amendment rights.