On Twitter, he renewed talk of his plan to ban Muslims from the U.S. for an indeterminate time. And he went after President Barack Obama.

As Obama stepped to the podium in Washington to address the nation early Sunday afternoon, Trump tweeted:

“Is President Obama going to finally mention the words radical Islamic terrorism? If he doesn’t he should immediately resign in disgrace!”

In his address Obama called the tragedy an act of terror and hate. He didn’t talk about religious extremists, nor did others, reluctant to inflame a stunned nation already on edge about attacks inspired by the Islamic State group.

Obama said the FBI would investigate the shootings in the gay nightclub as terrorism but that the alleged shooter’s motivations were unclear. He said the U.S. “must spare no effort” to determine whether Mateen had any ties to extremist groups.

Hours later, a law enforcement official confirmed to The Associated Press that Mateen had made a 911 call from the club, professing allegiance to the leader of Islamic State group, Abu Bakr al-Baghdadi.

The official was familiar with the investigation but not authorized to discuss the matter publicly and spoke on condition of anonymity.