“The FBI and DHS remain concerned about the potential for follow-on or retaliatory acts of violence following this attack, particularly given that individuals in some online communities have threatened, encouraged, or referenced acts of violence in response to the attempted assassination,” the bulletin said.

The warning comes amid what authorities had already determined was a “heightened threat” environment, with the country deeply polarized as the Republicans gather for their nominating convention in Milwaukee and the Democrats prepare for theirs in Chicago.

“This attack reinforces our assessment that election-related targets are under a heightened threat of attack or other types of disruptive incidents,” the bulletin said.

The agencies said that Thomas Matthew Crooks, the 20-year–old shooter in Saturday’s attack at the rally, had improvised explosive devices in his car as well as his home and ordered packages potentially containing hazardous material over the last several months.

Law enforcement officers survey the scene after the shooting in Butler, Pennsylvania, on July 13.
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Scott Goldsmith for POLITICO

Authorities have not yet determined what motivated Crooks, who was shot and killed by the Secret Service after he opened fire on the rally, killing one spectator and critically wounding two others.

In the lead-up to the November election, federal and state law enforcement agencies have stepped up efforts to prevent political violence and lone-wolf attacks against elected officials, government officials, candidates, law enforcement and the media. The Justice Department has vowed to relentlessly crack down on threats against election workers and elections facilities.

Threats across the political spectrum have proliferated. Supporters of Trump sent death threats and envelopes full of white powder to Manhattan District Attorney Alvin Bragg, whose office led the hush money prosecution against the former president. Others “swatted” Maine Secretary of State Shenna Bellows after she found Trump to be ineligible to appear on the state’s 2024 primary ballot.