WASHINGTON (AP) — President Joe Biden warned Sunday of the the risks of political violence in the U.S. after Saturday’s attempted assassination of former President Donald Trump, saying, “It's time to cool it down.”

Biden delivered short afternoon remarks from the White House after receiving a briefing on the investigation in the Situation Room. He called for the country to “unite as one nation” and a “thorough and swift" review and asked the public not to “make assumptions” about the shooter's motives or affiliations.

The president said he has also directed the U.S. Secret Service to review all security measures for the Republican National Convention, which begins Monday in Milwaukee. Hours later, Audrey Gibson-Cicchino, the Secret Service’s coordinator for the convention, said the weekend attack against Trump did not prompt any changes to the agency's security plan for the event and that officials “are fully prepared.”

In his remarks, Biden called the attack on Trump “not who we are as a nation.”

"It’s not American. And we cannot allow this to happen," he said. “Unity is the most elusive goal of all, but nothing is more important than that right now."

Biden planned to deliver extended remarks to the nation Sunday evening in an address from the Oval Office. His campaign said the president would touch on “the need for every American to come together to not just condemn, but put to an end to political violence in this country.”

In the meantime, the president said he and first lady Jill Biden were praying for the family of Corey Comperatore, a former fire chief who was shot and killed during the Trump rally Saturday night in Butler, Pennsylvania.

“He was protecting his family from the bullets," Biden said. "God love him.”

The president also said he'd had a “short but good conversation” with Trump in the hours after the shootings and that he was “sincerely grateful” that the former president is “doing well and recovering.”

Trump, who has called for national resilience since the shooting, posted on his social media account after Biden's remarks, “UNITE AMERICA!”

Actually achieving unity will be far more challenging, especially in the midst of a bitter presidential campaign. Biden's team is grappling with how to calibrate the path forward after the weekend attack on the very person he is trying to defeat in November's election.

Biden, who has set out to brand Trump as a dire threat to democracy and the nation’s very founding principles, put a temporary pause on such political messaging. Shortly after Saturday night's attack, Biden’s reelection campaign froze “all outbound communications” and was working to pull down its television ads.

The president also postponed a planned trip to Texas on Monday, where he was to speak on the 60th anniversary of the Civil Rights Act at the Lyndon B. Johnson presidential library. An NBC News interview between Biden and anchor Lester Holt will now occur at the White House, instead of in Texas, as initially planned.

Biden's campaign said that, after the NBC interview airs on Monday night, it and the Democratic National Committee “will continue drawing the contrast” with Trump over the course of the GOP convention — even though it remains unclear when ads would resume.

Biden also still plans to make a planned trip to Las Vegas, which will include a campaign event on Wednesday. Vice President Kamala Harris nonetheless postponed her planned campaign trip to Florida on Tuesday, where she had been set to meet with Republican women voters.

Trump, meanwhile, announced that he was moving up plans to go to Milwaukee and the Republican convention, where criticism of Biden and the Democrats is sure to be searing.

The weekend developments were only the latest upheaval in a campaign that has been extraordinarily topsy-turvy in recent weeks.

Biden’s shaky debate performance on June 27 so spooked his own party that some top surrogates and donors turned on him, and nearly 20 Democratic members of Congress called on the president to leave the race the bullseye.”

A person familiar with those remarks said the president was trying to make the point that Trump had gotten away with a light public schedule after last month's debate while the president himself faced intense scrutiny. The person spoke on the condition of anonymity to more freely discuss private conversations.

In the donor call, Biden said: “I have one job and that’s to beat Donald Trump ... I’m absolutely certain I’m the best person to be able to do that."

He continued: “So, we’re done talking about the debate. It’s time to put Trump in the bullseye. He’s gotten away with doing nothing for the last 10 days except ride around in his golf cart, bragging about scores he didn’t score … Anyway I won’t get into his golf game.”