In a span of just over 12 hours, horrific mass shootings left two American cities devastated and grieving, sparking calls for stricter gun laws and eliciting warnings of a growing threat from white supremacist violence. In El Paso, Texas, a gunman opened fire as customers crowded into a Walmart during the busy back-to-school shopping season Saturday morning, leaving 20 people dead and another 26 wounded. It was the second deadly shooting at a Walmart in less than a week.



Americans barely had time to process the scale of the tragedy on the nation's southwestern border when violence struck another community, more than a thousand miles away from El Paso in the Midwest.



In Dayton, Ohio, a gunman clad in body armor and carrying extra magazines opened fire in area popular for its nightlife, killing nine people and leaving 27 others wounded.

Shoppers exit with their hands up after a mass shooting at a Walmart in El Paso, Texas, U.S. August 3, 2019. Jorge Salgado | Reuters

Dayton's mayor said many more people likely would have died if it weren't for police patrolling the area, who killed the gunman in less than a minute. The gunman in the Dayton shooting has been identified as a 24-year-old white male named Connor Betts, a senior law enforcement official told NBC News.



As investigators searched for a motive in the Dayton massacre, police in El Paso began to assemble a picture of a gunman apparently motivated by a hatred for immigrants.



Police in El Paso detained a 21-year-old white male suspect named Patrick Wood Crusius, who comes from the Dallas area. The suspect is believed to have posted a racist diatribe in the online forum 8chan before the massacre, senior law enforcement officials told NBC News.



The document says the shooting "is a response to the Hispanic invasion of Texas" and praises the gunman who massacred 51 people at two mosques in Christchurch, New Zealand in March. The El Paso shooting is being treated as a domestic terrorism case, according to the U.S. Attorney for the Western District of Texas. Federal authorities are "seriously considering" bringing hate crime charges in the case, he said.

Shoes are piled outside the scene of a mass shooting including Ned Peppers bar, Sunday, Aug. 4, 2019, in Dayton, Ohio. Several people in Ohio have been killed in the second mass shooting in the U.S. in less than 24 hours, and the suspected shooter is also deceased, police said. John Minchillo | AP Photo

Democrats accuse Trump of complicity

Democratic presidential candidates roundly called for stricter gun laws to address the repeated mass shootings that have shaken the United States. Republican Texas Gov. Greg Abbott, in a press conference Saturday on the El Paso shooting, said the nation needed to address mental health issues. The shooting in El Paso has also reignited a bitter debate over President Donald Trump's rhetoric against migrants.



Trump condemned the shooting in El Paso "an act of cowardice" and said "there are no reasons or excuses that will ever justify killing innocent people."



But Democratic presidential candidate Beto O'Rourke, a former congressman from El Paso, called Trump a racist and said his rhetoric encourages violence like the shooting in El Paso.



"This president is encouraging greater racism and not just the racist rhetoric, but the violence that so often follows," O'Rourke said in an interview with CNN's "State of The Union" on Sunday.

Mourners taking part in a vigil at El Paso High School after a mass shooting at a Walmart store in El Paso, Texas, U.S. August 3, 2019. REUTERS/Jose Luis Gonzalez Jose Luis Gonzalez | Reuters