WASHINGTON — President Joe Biden on Sunday appealed for the country to “unite as one nation” after Saturday’s apparent attempted assassination of former President Donald Trump and said he was ordering an independent security review of the lead-up to the attack.

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Biden delivered brief remarks from the White House after receiving a briefing on the investigation in the Situation Room. He said he has directed the probe to be “thorough and swift,” and asked the country not to “make assumptions” about the perpetrator’s motives or affiliations.

Biden plans to deliver extended remarks to the nation Sunday evening in a prime-time address from the Oval Office.

Biden quickly denounced the shooting and talked to Trump in its aftermath. His campaign team, meanwhile, is grappling with how to manage the political implications of an attack on the man Biden hopes to defeat in the November election. He 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 in wake of Trump rally shooting, the White House said.