Armed with assault rifles and clad in combat gear, two white men methodically gunned down more than 30 people over the weekend, underscoring fears that "white terrorism" is now the main threat in the U.S.

The shooter, a 21-year-old white man identified in media reports as Patrick Crusius, killed 22 people before surrendering to police. Eight of those killed in the attack were Mexican citizens, according to the Mexican government.

An online manifesto attributed to the assailant railed against a "Hispanic invasion" and referred approvingly to the March 15 massacre by a white supremacist at two mosques in Christchurch, New Zealand. The four-page statement uploaded to 8chan, a largely unmoderated online message board often used by extremists, called the El Paso attack "a response to the Hispanic invasion of Texas."

It also expressed support for the Christchurch terrorist. At least 51 Muslims were gunned down March 15 by Australian-born white supremacist Brenton Tarrant who has been slapped with 51 counts of murder and 40 attempted murder charges, along with terrorism.

Thirteen hours after the El Paso attack, another white man is accused of spreading terror in the midwestern city of Dayton, Ohio, killing nine people including his sister, authorities said. Police named him as Connor Betts, 24. While police say the motive is still unclear, six of the nine people killed in Dayton were black.

For years, there has been growing warning that the huge shifting of intelligence and security assets toward fending off foreign threats after the 9/11 attacks had come at the expense of much-needed attention to domestic dangers. FBI Director Christopher Wray testified last month in Congress that a majority of the domestic terrorism cases the bureau had investigated in the previous nine months were motivated by some version of "white supremacist violence."

Confronting domestic terrorism is an urgent issue for law enforcement at a time when white supremacists and like-minded extremists are causing more murders, including a rampage at a Pittsburgh synagogue that killed 11 last October, than Americans inspired by foreign groups. The FBI made about 90 domestic terrorism arrests in the first three quarters of the year and has hundreds of open cases.

In 2016, the New America Foundation claimed that white supremacists have been responsible for more deaths in the U.S. than foreign terror organizations, including Daesh and al-Qaida, after 9/11, citing several examples such as the Wisconsin Sikh temple shooting in 2012. Attacks such as the San Bernardino shooting or the Boston Marathon in 2013 also received a lot of public attention. The Charleston Church massacre, the chilling slaughter of nine black church members by an avowed white supremacist called Dyton Roof in 2016, was one of the biggest examples of rising hate crimes in the country.

In 2017 and 2018, the center continued to reveal that violence from the far-right claimed more victims in the U.S. than attacks by foreign terror groups. A New York Times article published on Aug. 5 drew parallels between the rise of Daesh and white nationalist terrorism, citing similarities between the two violent groups.