Two mass shootings in 24 hours put the US focus back on to gun control and, given the anti-immigrant views of a shooter in Texas, the dangers of hate speech.
In his first verbal response to the killings, in which 29 people were killed, President Donald Trump said that “hate has no place” in the US.
Gun control has mostly been a mostly secondary theme on the Democrats’ 2020 campaign trail until now.
Some have written it off as a lost cause after years of violent incidents with little policy response from legislators or others.
Mr Trump said on Sunday that he had spoken to Attorney General William Barr and others.
“Hate has no place in our country and we’re going to take care of it,” Mr Trump said in New Jersey as he boarded Air Force One after a weekend at his golf club in Bedminster.
He said gun violence had been “going on for years".
Presidential candidates including Beto O’Rourke, the former Congressman from El Paso, South Bend Mayor Pete Buttigieg and former San Antonio Mayor Julian Castro linked Mr Trump's tirades and violent behaviour.
Police on Saturday arrested a Texas man, 21, suspected of opening fire with an assault rifle at a Walmart shop in El Paso, Texas, killing at least 20 people.
The suspect drove hundreds of miles from his near home near Dallas to carry out the attack in the heavily Hispanic city on the US-Mexican border.
The Department of Justice is treating the case as domestic terrorism, spokeswoman Kerri Kupec said on Twitter. A conviction could mean the death penalty.
Authorities are investigating a possible link to an anti-immigrant document published online shortly after the killings, with anger directed against Mexicans.
The attacks gave a new impetus to critics of Mr Trump’s harsh speeches on immigration.
Three Mexicans were killed in the El Paso shooting, Mexican President Andres Manuel Lopez Obrador said in a Twitter video.
Less than 24 hours after the El Paso shooting, a gunman in body armour and with at least 100 rounds of ammunition killed nine people and injured dozens in a popular nightlife district of Dayton, Ohio.
The suspect, who was killed, was identified on Sunday as Connor Betts, in his twenties, of the nearby town of Bellbrook, Ohio. No motive was identified.
Mr Buttigieg said the shootings were wake-up calls for tighter gun control and battling white nationalist terrorism.
"We've got to call that what it is if we're going to fight it," he told CNN's State of the Union. "We have a president who made his career politically on demonising Mexicans.
"We’re seeing reports that the shooter yesterday had as his goal shooting as many Mexicans as possible. You don’t have to use a lot of imagination to connect the dots here.”
Mr Castro, the former secretary of housing and urban development, said Mr Trump had “given licence for this toxic brew of white supremacy to fester more and more”.
Mr Trump tweeted that the El Paso killings were “an act of cowardice”, and said there were “no reasons or excuses that will ever justify killing innocent people".
The White House ordered flags flown at half staff on US public buildings and military posts for five days.
Mr Trump launched his presidential bid in June 2015 with a speech that slammed immigrants from Mexico as drug dealers, criminals and rapists.
Since then, anti-immigrant tirades and a focus on the US-Mexican border have been main focuses of his administration.
Mr Trump has described the southern border as “a pipeline for vast quantities of illegal drugs including meth, heroin, cocaine and fentanyl".
He has termed gang members “animals” and sent troops to the southern border to “stop the attempted invasion of illegals". He has also said in tweets and at rallies that the US is full.
In recent weeks Mr Trump has increased racially charged speech against Democratic legislators and others in an a bid to animate his base for the 2020 election.
Representative Tim Ryan of Ohio, another Democratic candidate for the White House, said on Fox News that Mr Trump’s "type of toxicity has permeated the whole country to where some jackass in Texas drives 10 hours to go shoot Mexicans".
Last week, faith leaders from the National Cathedral in Washington, who typically stay far from the political fray, said Mr Trump’s “violent dehumanising words” attacking minority politicians and others risked disastrous consequences.
Mr O’Rourke, who left the campaign trail to return to his home town on Saturday, was asked on ABC whether he was suggesting Mr Trump bore responsibility for the El Paso events.
“I am, because he does,” he said. “He doesn’t just tolerate, he encourages the kind of open racism and the violence that necessarily follows, that we saw here in El Paso.”
Mr Trump’s racial attacks are so common that most other business has been eclipsed, keeping the issue foremost in voters’ minds before the elections.
His Twitter attacks on congressman Elijah Cummings, a black Democrat from Maryland, prompted the leaders at the National Cathedral, site of four presidential funerals, to post the essay, Have we no Decency? A Response to President Trump, on July 30.
“Violent words lead to violent actions,” the Cathedral’s three most senior religious leaders said.
“They are a clarion call, and give cover, to white supremacists who consider people of color a sub-human ‘infestation’ in America.
"They serve as a call to action from those people to keep America great by ridding it of such infestation.”
Congress has failed to pass any meaningful gun restrictions since the 2012 shooting at the Sandy Hook Elementary School in Connecticut.
The deaths of 26 people, including 20 children aged 6 and 7, was considered a tipping point for measures to restrict access to guns.
Mr Trump banned bump stocks, which allow a semi-automatic weapon to fire like a machinegun, after a massacre at a Las Vegas concert in October 2017 killed almost 60 people.
He said after a mass shooting in Virginia in June that he would “seriously look” and banning gun silencers, but no action was taken.
Acting White House chief of staff Mick Mulvaney said that the Texas shooter’s manifesto said he had developed his anti-immigrant views years ago.
Mr Mulvaney said it was unfair to blame Mr Trump for the acts of “sick, sick people“ and a societal “cancer” that was present before the administration was elected.
“There are people in this country this morning thinking that President Trump was happy by this,” he told ABC.
“That’s a sad, sad state of this nation. He’s angry. He’s upset. He wants it to stop.”
But Mr Castro spoke about the responsibility of the commander in chief and how, unlike most presidents, Mr Trump has chosen not to try to unite people.
He “made a clear choice to divide people for his own political benefit" the Democrat said.
“There’s one person that’s responsible directly for that shooting in El Paso. And that’s the shooter,” Mr Castro said.
“At the same time, as our national leader, you have a role to play in either fanning the flames of division or trying to bring Americans of different backgrounds together.”
On Sunday, Mr Trump said he had spoken to many people and that his administration had “done much more than most administrations” on the issue of gun violence.
"Perhaps more has to be done,” he said.
