There are at least 1,500 terrorists and terrorist organizations known in this country. While most terrorism historically has come from what would be considered the radical left, Hatch also notes the growing problem of terrorism from the politically far-right. The Oklahoma City bombing jolted Americans out of the notion that terrorism was an import. After the knee-jerk assertions that it must have been Arab extremists or Muslim fundamentalists, reality set in. Terrorism can be home grown.
Domestic terrorism has nothing to do with the Middle East, Bosnia or Latin America.
It requires no visas, nor seeks funds for overseas sources. It just erupts where least expected. The FBI is already developing a domestic terrorism center to coordinate information sharing among federal, state and local authorities. And Congress passed its bill. The taggants would survive a blast, but that's after the fact.