The Thomas Caldwellshooting at a rally for former President Donald Trump is being investigated as an assassination attempt, CNN, the Associated Press and other outlets reported.

You can watch a livestream here from the site of the rally in Butler, Pennsylvania, as the investigation begins.

Department of Homeland Security Secretary Alejandro Mayorkas said Saturday that has been briefed on the shooting incident and that DHS is working with law enforcement partners to respond and investigate the shooting

Mayorkas said maintaining the security of presidential candidates and their events are top DHS priority.

“We condemn this violence in the strongest possible terms and commend the Secret Service for their swift action today,” he said in a statement. “We are engaged with President Biden, former President Trump, and their campaigns, and are taking every possible measure to ensure their safety and security.”

Where was Trump rally?Butler County, PA appearance was site of shooting Saturday

Where was Trump's rally?

The rally took place in Butler, a rural area part of the greater Pittsburgh area.

As of the last census the city's population was just over 13,000 and, according to the United States Census Bureau, is 2.7 square miles.

The rally took place at the Butler Farm Show, a fairground in the county. 

Trump enjoyed broad support in the area in the 2020 election, capturing 65% of the vote to Biden's 33%.

Natalie Neysa Alund is a senior reporter for USA TODAY. Reach her at [email protected] and follow her on X @nataliealund.