WASHINGTON — President Trump called the Las Vegas attack "an act of pure evil" and called for national unity in the wake of the deadliest mass shooting in modern U.S. history.

"Hundreds of our fellow citizens are now mourning the sudden loss” of a parent, child, friend or other family member, Trump said at the White House on Monday. "We cannot fathom their pain, we cannot imagine their loss."

Trump announced that he would visit Las Vegas on Wednesday, and he said the FBI and Department of Homeland Security are working closely with local authorities. He praised the local police department and first responders for their quick response to the attack.

On Sunday night, a gunman opened fire from a hotel room above a packed outdoor concert in Las Vegas, an attack that killed at least 50 and wounded at least 400 more. White House press secretary Sarah Huckabee Sanders said Trump was briefed early Monday.

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It is the first mass killing under Trump's watch as his ability to console the nation is already being tested by his administration's response to hurricanes in Texas, Florida and Puerto Rico. A gunman opened fire on a congressional baseball practice in June, but no victims were killed in that incident.

There were at least 14 mass shootings during President Obama's two terms, a source of significant frustration for the president, which he described in 2015 as having "no parallel anywhere else in the world."

In his response, Trump made no similar references to the phenomenon of mass gun shootings in America and whether anything can be done to prevent them. "In times such as these I know we are searching for some kind of meaning in the chaos, some kind of light in the darkness. The answers do not come easy.”

"We pray for the entire nation to find unity and peace," said Trump, who issued a proclamation that the U.S. flag be flown at half staff through Oct. 6.

Vice President Pence also extended sympathies to the victims of the Las Vegas shooting via a series of tweets.

"To the courageous first responders, thank you for your acts of bravery," Pence said in one tweet.

Clark County Sheriff Joe Lombardo said the shooter, identified as Stephen Paddock, 64, was found dead by officers who stormed his 32nd-floor room at the Mandalay Bay Resort and Casino.

The shooting is also likely to lead to renewed calls by congressional Democrats for increased gun restrictions, including universal background checks. Yet with Republicans in control of both chambers and the White House, those efforts are unlikely to gain traction.

Since 1980, there have been at least 56 mass shootings, defined as including 3 or more fatalities, where the shooter used high-capacity ammunition magazines, according to the Violence Policy Center.

This volume corresponds with a shift toward high-capacity firearms being marketed by gun manufacturers. In 1980, semi-automatic pistols accounted for only 32% of the handguns produced in America. By 1991, this proportion had jumped to 74%, according to VPC. Shares of gun makers jumped 5% in early trading Monday.

Trump is still scheduled to travel Tuesday to Puerto Rico to review hurricane recovery efforts.

His response to the Las Vegas tragedy was more focused on sympathy for the victims, in contrast to his statements as a candidate in the aftermath of mass shootings.

After a mass shooting at an Oregon community college in 2015, Trump said that fewer people would have died if more of the victims had their own guns. He made the same argument after the Orlando night club shooting a year later, saying it would have minimized the death count if others “had guns strapped to their waists or strapped to their ankle.”

In omitting the incidence of mass shootings in the U.S., Trump sent a clear signal his administration does not see a link between these incidents and the relative ease with which individuals in the U.S. can obtain high-powered weapons and firearms originally conceived for battlefield use.

Trump's response is also in contrast with the previous Democratic-led administration.

Before Sunday night, the deadliest mass shooting in modern U.S. history was in June 2016 at the Pulse night club in Orlando, in which 49 lives were lost.

At the time, Obama called it "a further reminder of how easy it is for someone to get their hands on a weapon that lets them shoot people in a school, or in a house of worship, or a movie theater, or in a nightclub." He also said "we have to decide if that’s the kind of country we want to be. And to actively do nothing is a decision as well."