Within days of the Sept. 11 terrorist attacks, the United States government began writing new laws, reinterpreting old ones and crafting aggressive new policies to defeat Al Qaeda and other Islamist terrorist groups.

In the aftermath of the deadly shootings this weekend, President Trump on Monday promised “with urgent resolve” to press a similar whatever-it-takes strategy to investigate and prevent white-supremacist violence and hate crimes. The F.B.I. has said that such racially motivated domestic terrorism now accounts for more deaths and arrests in the United States than Islamist terrorism.

“We can and will stop this evil contagion,” Mr. Trump said. He ordered the F.B.I. to identify the necessary tools and promised to deliver “whatever they need.”

While thin on specifics, Mr. Trump’s remarks raised the prospect of empowering the Justice Department to investigate American hate groups with the vigor that it has brought to the fight against international terrorism.