WASHINGTON – President Barack Obama decried the deadliest mass shooting in American history on Sunday as a terrorist act targeting a place of “solidarity and empowerment” for gays and lesbians. He urged Americans to decide “if that’s the kind of country we want to be.”

Hours after a gunman killed at least 50 people in Orlando, Obama said the FBI would investigate the nightclub shooting as terrorism, but said the alleged shooter’s motivations were unclear. He said the U.S. “must spare no effort” to determine whether the suspect, identified by authorities as Omar Mateen, had any ties to extremist groups.

“What is clear is he was a person filled with hatred,” Obama said of the alleged shooter. He added: “We know enough to say that this was an act of terror and an act of hate. And as Americans, we are united in grief, in outrage, and in resolve to defend our people.”

Obama had planned to travel to Wisconsin on Wednesday for his first campaign appearance of the 2016 race, a joint rally with Hillary Clinton in Green Bay, Wisconsin. But Clinton’s campaign and the White House said that event was being postponed in light of the attack.

The president, who has proclaimed June as Lesbian, Gay, Bisexual, and Transgender Pride Month, called the attack “heartbreaking” for the LGBT community. He said the site of the shooting was more than a nightclub because it was a place where people came “to raise awareness, to speak their minds and to advocate for their civil rights.”

“The shooter targeted a night club where people came together to be with friends to dance and to sing — to live,” Obama said.

For Obama, the hastily arranged remarks were the latest in what’s become a tragically familiar routine. Since he took office in 2009, Obama has appeared before cameras more than a dozen times following mass shootings and issued written statements after many others.

The president made no new, specific call for stricter gun laws. Though he lamented “how easy it is” for people to get their hands on weapons, Obama appeared resigned to the likelihood that he’ll be unable as president to substantially address the mass shootings that have proliferated in recent years.

“We have to decide if that’s the kind of country we want to be,” Obama said. “To actively do nothing is a decision as well.”

After a gunman in Newtown killed 20 first graders and six adults in 2012, Obama dedicated much of the start of his second term to pushing legislation to expand background checks, ban certain assault-style weapons and cap the size of ammunition clips. That measure collapsed in the Senate, and since then, the political makeup of Congress have made new gun laws appear out of reach. Still, Obama has sought to take incremental steps using his own authority to tighten rules for obtaining a gun.

Obama spoke from the James S. Brady Press Briefing Room, named after the former press secretary who was shot and permanently disabled in an assassination attempt on President Ronald Reagan.

He also signed a proclamation on Sunday ordering flags to be flown at half-staff until sunset on Thursday in honor of the victims.

Vice President Joe Biden canceled a planned trip Sunday to Miami to hold a fundraiser for Rep. Debbie Wasserman Schultz, D-Fla. Biden’s office said he would remain at his family home in Delaware while receiving updates about the shooting before returning to Washington in the evening.

Kevin Freking and Josh Lederman of the Associated Press wrote this report. Associated Press writer Kathleen Hennessey contributed to this report.