Like past mass shootings, the massacre in Florida swiftly reignited a national debate about access to assault weapons and possible changes to gun control laws. Authorities believe Cruz used an AR-15-style rifle, which is frequently used in American mass shootings.
Trump and Republican lawmakers have repeatedly pushed back against calls to tighten gun laws after previous mass shootings. The GOP-controlled Congress has taken few concrete steps to address access to guns or improving mental health following past massacres, including the deadliest shooting in modern American history that took place in Las Vegas last year.
On Thursday, House Speaker Paul Ryan cautioned against swift action on gun rules.
"This is not the time to jump to some conclusion, not knowing the full facts," the Wisconsin Republican told reporters, adding that lawmakers need to look at "gaps" in laws that may allow mentally ill people to get guns.
Last February, Trump quietly signed a bill to scrap an Obama-era regulation making it tougher for people with mental illnesses to buy a gun. On Thursday morning, he tweeted that signs emerged that Cruz was "mentally disturbed" and questioned why his classmates and community did not report him to authorities.
Some federal officials, even within Trump's administration, urged Congress to consider new solutions following the shooting. On Thursday, Treasury Secretary Steven Mnuchin urged Congress to "look at" possible fixes for gun violence.
Senate Democratic leader Chuck Schumer urged his colleagues to "resolve to do something, something, about the epidemic of gun violence in this country."
Trump's predecessor President Barack Obama tweeted that "we are not powerless" to stop gun violence, adding that "caring for our kids is our first job."
"And until we can honestly say that we're doing enough to keep them safe from harm, including long overdue, common-sense gun safety laws that most Americans want, then we have to change," he wrote.
Trump ordered flags to be flown at half-staff until sunset Monday, saying in a statement: "Our Nation grieves with those who have lost loved ones in the shooting at the Marjory Stoneman Douglas High School in Parkland, Florida."