President Joe Biden on Sunday repeated calls for national unity in the wake of Saturday's assassination attempt on former President Donald Trump.

       "Last night I spoke with Donald Trump. I am sincerely grateful that he’s doing well, and recovering. We had a short but good conversation. Jill and I are keeping him and his family in our prayers," he said, speaking about the assassination aftermath before reporters gathered the White House Roosevelt Room.

       "An assassination attempt is contrary to everything we stand for as -- as a nation, everything. It's not who we are as a nation. It's not American. And we cannot allow this to happen," he continued.

       U.S. President Joe Biden delivers a statement a day after Republican challenger Donald Trum...Show more ---Show more

       Nathan Howard/Reuters

       "Unity is the most elusive goal of all, but nothing is important than that right now, unity. We’ll debate and we’ll disagree, it's not-- that's not going to change. But it's going to -- we're going to not lose sight of the fact who we are as Americans," he said.

       He cautioned against speculation about the shooter's motive, saying it wasn't yet known.

       And he said he had ordered an independent review of how security was handled at the political rally in Pennsylvania amid congressional Republican demands for investigative hearings.

       He ended by saying he would speak to the nation Sunday night and the White House said afterward his address from the Oval Office would take place at 8 p.m. ET.

       Biden, who was flanked by Garland, Mayorkas and Vice President Kamala Harris, did not take questions.

       President Joe Biden speaks from the Roosevelt Room of the White House in Washington, July...Show more ---Show more

       Susan Walsh/AP

       MORE: Biden and Trump speak after he says 'no place in America for this kind of violence'

       He had been briefed shortly before in the White House Situation Room by Attorney General Merrick Garland. Homeland Security Secretary Alejandro Mayorkas, FBI director Christopher Wray, national security adviser Jake Sullivan and Secret Service Director Kim Cheatle.

       The White House posted a photo of the briefing on X.

       Biden has had to tread carefully since news of the Trump shooting first broke because not only is he president -- but also a candidate and Donald Trump's political opponent.

       He must show he's in command of the crisis as well amid growing questions about his mental and physical fitness for the job.

       President Joe Biden speaks after his Republican opponent Donald Trump was injured followin...Show more ---Show more

       Manuel Balce Ceneta/AP

       MORE: Trump shooting live updates: Gun traced to suspect's father, was legally purchased

       Informed shortly after the shooting happened, he initially put out a statement -- after some basic facts became known -- saying he was "grateful" that Trump was "safe."

       He then made hastily arranged remarks to reporters and the nation on live television -- saying he had tried to phone the former president -- whom he notably called "Donald" -- condemning the attack and calling for unity.

       "There's no place in America for this kind of violence. It’s sick. It’s sick. It’s one of the reasons why we have to unite this country," he said.

       "But the idea, the idea that there's political violence or violence in America like this, is just unheard of, it’s just not appropriate. We – everybody, everybody must condemn it," he said.

       President Joe Biden deboards from Air Force One as he arrives at Joint Base Andrews in Md., July 14, 2024.

       Tom Brenner/Reuters

       He then quickly changed plans and flew back from Delaware to the White House.

       When he arrived at Joint Base Andrews, it was notable how close Biden’s top Secret Service agent was to him as he stepped off Air Force One, staying just a few steps away as the president walked down the steps.

       Typically, Biden makes it to the bottom of those steps before his security detail steps off the plane.

       Lafayette Park, directly in front of the White House, remained closed Sunday morning as the Secret Service posture was notably heightened around the White House.

       Sunday afternoon, the White House said said Biden was rescheduling his planned Monday trip to Austin, Texas, where he was set to deliver the keynote address at a commemoration for the 60th Anniversary of the Civil Rights Act at the LBJ Presidential Library.