White House spokeswoman Sarah Huckabee Sanders called the massacre a "horrific tragedy."
A lone gunman, identified as Stephen Paddock, 64, opened fire during the Route 91 Harvest Festival, a three-day country music event attended by thousands, killing at least 50 and injuring 200, police said. Police shot him to death on the 32nd floor of the nearby Mandalay Bay Resort, Clark County Sheriff Joseph Lombardo said in a news conference early Monday.
Trump in the past has speculated on the motive for violence, before any official information had been confirmed. He decried the explosion at a London tube station last month as the work of a "loser terrorist" and used the attack to promote his own travel ban on Muslim-majority countries.
At other times, the president has been conspicuously silent in the face of atrocity. It took him four days to comment on the white supremacist rally that descended upon Charlottesville, Virginia, in August.