Addressing the nation about two hours after the shooting, Biden said he was relieved that Trump is reportedly "doing well." He said he had been unable to reach Trump before his remarks, but the White House said he did speak to Trump several hours later.

"We cannot allow this to be happening," Biden said. "The idea that there's violence in America like this is just unheard of."

Biden, speaking without a teleprompter, said he was waiting for additional information before formally calling the attack an attempted assassination on the former president.

"I have an opinion, but I don't have any facts," he told reporters, pledging to provide updates as he learns more.

Later Saturday, he was returning to the White House, cutting short a weekend stay in Delaware to monitor the unfolding situation.

The president delivered remarks from the White House's emergency briefing room in Rehoboth Beach, Delaware, which is set up whenever the president travels to allow him to deliver remarks to the country in a matter of minutes. He was spending the weekend at his beach home and was at a nearby church for mass when the shooting occurred.

As he left the church, reporters asked if the president had been briefed about the shooting. Biden turned toward reporters with a serious look on his face but replied simply, "no," before stepping into his motorcade.

Biden received an "initial briefing" from aides moments later then convened security officials for a more in-depth update from Kimberly Cheatle, the director of the United States Secret Service, Homeland Security Secretary Alejandro Mayorkas, and White House homeland security adviser Liz Sherwood-Randall.

Many Republicans quickly blamed the violence on Biden and his allies, arguing that sustained attacks on Trump as a threat to democracy have created a toxic environment. They pointed in particular to a comment Biden made to donors on July 8, saying "it's time to put Trump in the bullseye."

There was no immediate information on the shooter or their motivations.

The Biden campaign said Saturday that it was pausing all messaging to supporters and working to pull down all of its television ads as quickly as possible in light of the shooting.

Vice President Kamala Harris said in a statement that she was also briefed, adding that she and her husband "are relieved" that Trump was not seriously inured.

"We are praying for him, his family, and all those who have been injured and impacted by this senseless shooting," she said.