2. A sudden focus on domestic terrorism.

Since the Sept. 11 attacks, more Americans have died in domestic terrorist attacks than in international terrorist attacks. And the F.B.I. says that domestic attacks are increasingly motivated by white supremacist ideology.

But even with President Trump’s promise to provide federal authorities with “whatever they need,” officials and analysts say that law enforcement agencies combating domestic terrorism may have difficulty adopting the same kind of aggressive efforts used abroad after Sept. 11. Above, F.B.I. agents gathered evidence at the Walmart attacked Saturday in El Paso.

One issue is how much more information tech companies would be willing to share with the police about their customers. Another is the politically volatile mix of race, identity and violence of domestic cases, especially during a presidential campaign.