El Paso, Texas (CNN) Two mass shootings within 24 hours, one of which is being investigated as a hate crime, have further inflamed the already heated political conversation around guns and immigration in the United States.

Trump's critics had long warned of the environment they say is being fostered by his demonization of immigrants and racist attacks on political opponents who are people of color.

On Sunday, two cities were grieving after mass shootings left 20 slain in El Paso, Texas , and nine killed in Dayton, Ohio . Investigators are examining document they believe the alleged gunman in El Paso posted to an online message board. The writing is filled with white nationalist language and racist hatred toward immigrants and Latinos, blaming immigrants and first-generation Americans for taking away jobs.

Former Texas Rep. Beto O'Rourke -- who canceled his campaign schedule to return home to El Paso immediately after the shooting, visiting with victims on Saturday and Sunday -- called Trump a white nationalist.

"The things that he has said both as a candidate and then as the president of the United States -- this cannot be open for debate," he said on CNN.

"We have a problem with white nationalist terrorism in the United States of America today," O'Rourke said, adding that "these are white men motivated by the kind of fear that this president traffics in."

Julián Castro, the former mayor of San Antonio and Housing and Urban Development secretary, said Trump "fans the flames of bigotry and white supremacy."

"Now we see the result: a rise in white nationalism and domestic terrorism directed at people based on their race, ethnicity, and religion," he said.

New Jersey Sen. Cory Booker said Trump "is responsible because he is stoking fears and hatred and bigotry."

And Pete Buttigieg, the mayor of South Bend, Indiana, said Trump is "condoning and encouraging white nationalists," adding that Trump "made his career, politically, on demonizing Mexicans and now we're seeing reports that the shooter yesterday had his goal as killing as many Mexicans as possible."

Trump's record on race and immigration

Trump's racism has been on display throughout his political life. Prior to running for president, he pushed "birtherism," falsely questioning the birth place of Barack Obama, the nation's first African American president. As a candidate, he referred to Mexican immigrants as "rapists" and called for banning all Muslims from entering the United States.

In office, Trump reacted to the death of a protester during a white supremacists' march in Charlottesville, Virginia, by saying there had been "very fine people on both sides." This month, he attacked four female Democratic congresswomen, all women of color, saying they should "go back" to the countries they came from and then standing by as attendees of a campaign rally, jeering one of the lawmakers, chanted, "Send her back!"

His hard-line immigration tactics on the southern border included a zero-tolerance family separation policy that led to children being removed from their parents and in migrants being kept in cages in unsanitary conditions that were on display weeks ago when Vice President Mike Pence toured a detention facility.

"President Trump's hateful and bigoted words have resulted in hateful and deadly consequences," said Janet Murguía, the president of UnidosUS.

"President Trump is pushing anti-immigrant hate into the mainstream," said Heidi Beirich, the director of the Southern Poverty Law Center's Intelligence Project.

But already, the same sequence that has followed mass shootings for years in the United States was beginning to play out. Democrats were calling Sunday for new gun restrictions, but Republicans showed no immediate willingness to take legislative action to attempt to curb gun violence.

Democratic presidential candidates and congressional leaders have long advocated for a series of gun control measures, including closing loopholes that allow firearms to be purchased without background checks, banning the sale of automatic weapons and ending the gun industry's immunity from civil liability when firearms they manufactured are used to kill.

Republicans react to mass shootings

But already on Sunday, there were familiar signs that Republicans in Congress -- who control the Senate and therefore can block any legislation -- are unlikely to advance significant new gun control measures in Washington or in statehouses. Republicans largely responded to the shootings without detailing any specific steps they would take to attempt to limit future gun violence.

House Minority Leader Kevin McCarthy, a California Republican , placed blame for mass shootings on "these video games that dehumanize individuals" -- despite the same video games' availability in countries without the same mass shooting epidemic -- in an interview Sunday on Fox News.

Asked if Senate Majority Leader Mitch McConnell, a Kentucky Republican, is open to dealing with gun violence legislatively in any way, his spokesman told CNN: "If the leader issues any additional statements I'll be sure to forward them to you."

Texas Gov. Greg Abbott said at the state level, the strongest area of agreement is on addressing mental health issues -- not implementing new gun restrictions.

"I think we need to focus more on memorials before we start the politics," Abbott said Saturday.

Ivanka Trump, the President's daughter and a White House adviser, and Texas Sen. Ted Cruz both tweeted condemnations of "white supremacy."

The President, meanwhile, tweeted that he had ordered flags to be flown at half-staff on federal buildings in honor of the victims of the two shootings. "Melania and I are praying for all those impacted by this unspeakable act of evil!" he tweeted.

White House chief of staff Mick Mulvaney insisted Trump deserves no blame for the El Paso, Texas, massacre despite his rhetoric.

"People are going to hear what they want to hear," Mulvaney said. "My guess is this guy's in that parking lot out in El Paso, Texas, in that Walmart doing this even if Hillary Clinton is president."

Others lashed out at the Democrats who had condemned Trump's incendiary rhetoric.

Kellyanne Conway, a White House counselor, tweeted: "Finger-pointing, name-calling & screaming with your keyboards is easy, yet... It solves not a single problem, saves not a single life."

Ronna McDaniel, the chairwoman of the Republican National Committee, took aim at O'Rourke on Twitter after the former El Paso congressman called Trump a white nationalist.

"A tragedy like this is not an opportunity to reboot your failing presidential campaign. This is disgusting and wrong," she tweeted.

O'Rourke's campaign manager, Jen O'Malley Dillon, responded: "What's disgusting and wrong is carrying water for a racist President whose very words inspired this violence. A real President would show leadership to a grieving community, seek solutions, and speak truth. That's what Beto's doing today."