WASHINGTON — FBI Director Christopher A. Wray assured Congress last month that his agents were aggressively combating domestic terror threats from a broad array of extremist groups.

“The FBI, working with our state and local law enforcement partners,” he said, “is all over this.”

But the bureau is now scrambling to investigate two incidents of possible domestic terrorism — a mass shooting in Gilroy, Calif., followed days later by a far more deadly attack in El Paso, Texas — that appears to undercut Wray’s assertions and raise questions about whether the FBI is doing enough to identify and stop murderous plots by home-grown fanatics with no ties to foreign terrorist organizations.

Some former law enforcement officials and Democratic lawmakers contend federal agencies have been caught flat-footed by a surge in mass shootings by white supremacists and other extremists targeting minorities, immigrants and religious groups.

Indeed, the gunman who killed 22 people at a Walmart store in El Paso on Aug. 3 pushed the total number of victims slain in domestic right-wing terrorism since 2002 to 109. That’s more than the 104 people killed on U.S. soil by zealots linked to al-Qaida or other foreign Islamist groups, the chief FBI focus since the terrorist attacks of Sept. 11, 2001.

“The FBI has been slow to react to this, to realign resources,” said Daryl Johnson, a former Homeland Security analyst who wrote a controversial 2009 memo warning of the rise of right-wing extremism, sparking a political backlash. His unit was later disbanded and the department’s work on violent right-wing extremism was halted.

“This problem is growing,” added Johnson, who recently published “Hateland,” a book on the threat. “This is a persistent problem that needs to be addressed.”

By any measure, the dangers posed by domestic terrorists have been building for years.

The FBI arrested 115 domestic terrorism suspects in fiscal 2018 and appears on pace to arrest as many this year. The vast majority, agents said, are driven by racist and anti-government ideology.

A senior FBI counterterrorism official, speaking on the condition of anonymity to brief reporters in May, said the bureau had recorded a “significant” rise in cases involving “racially motivated extremism” since last fall. He declined to provide specifics, or attribute what might be behind the spike.

Overall, FBI agents have arrested more suspects in domestic terrorism investigations in the last three years than in probes with an international nexis: 355 people versus 310. The FBI did not provide a breakdown of charges lodged against the suspects, or the status of their cases.

The FBI currently has about 850 open investigations into domestic terrorism, officials said, although that tally is down slightly from last year.

Outside experts said the FBI needs to do a better job of infiltrating extremist groups and identifying so-called lone wolves, such as the alleged El Paso gunman, who told police he became self-radicalized after reading and posting racist, anti-Semitic and xenophobic screeds on social media and the internet.