Trump shooting updates: Shooter flew drone near site hours before shooting

The Bethel Park School District confirmed on Sunday that the suspected gunman was a graduate of Bethel Park High School and graduated with the Class of 2022.

"The school district wishes to express its sincere wishes for a speedy and full recovery for Mr. Trump and for those in attendance at the Saturday event who may have been physically harmed or emotionally impacted by these tragic events. We offer special condolences to the family of at least one attendee who was killed. Our thoughts and prayers are with you at this difficult time," the district said in a statement.

-ABC News' Sasha Pezenik

In an internal Trump campaign memo sent to staff, and obtained by ABC News, Susie Wiles and Chris LaCivita ask staff to avoid the campaign offices in D.C. and West Palm Beach and say they're enhancing the armed security presence with 24/7 officers on site.

Wiles and LaCivita said the Republican convention will continue as planned and asked staff not to comment publicly on what occurred.

"We condemn all forms of violence, and will not tolerate dangerous rhetoric on social media," they said in the memo.

-ABC News' Katherine Faulders

Former President Donald Trump on Sunday called for Americans to "stand United" after an assassination attempt at his Pennsylvania rally left one person dead.

It was "God alone who prevented the unthinkable from happening," the former president said in a post on the Truth Social platform. Trump previously said he was struck in the ear by a bullet.

Trump added, "In this moment, it is more important than ever that we stand United, and show our True Character as Americans, remaining Strong and Determined, and not allowing Evil to Win."

-ABC News' John Santucci and Kevin Shalvey

Officials on Sunday will be reexamining security plans for the Republican National Convention to determine whether any changes need to be made in light of Saturday’s assassination attempt, a senior federal official told ABC News.

The convention is scheduled to begin Monday in Milwaukee, Wisconsin.

Security details could be altered ahead of the event, including the number of agents and snipers deployed to the locations used by people under U.S. Secret Security protection.

Officials may also decide whether events outside the convention perimeter should be canceled, moved or have enhanced security measures.

-ABC News’ Aaron Katersky, Josh Margolin and Pierre Thomas