WASHINGTON (AP) — President Donald Trump is calling on federal authorities to do a better job identifying violent extremists. But that won't be easy.

Federal investigators looking to prevent acts of domestic terrorism, like the massacre of 22 people in El Paso on Saturday, have fewer tools and authorities at their disposal than they would if they were up against someone tied to an international organization such as al-Qaida.

That challenge has revived questions about whether the FBI is adequately positioned to confront a white nationalist threat.

David Gomez, a former FBI counterterrorism supervisor, says existing laws "are not designed around the FBI being able to prevent these actions."

The FBI has made about 90 domestic terrorism arrests in the first three quarters of the year and has hundreds of open cases.