Brad Raffensperger, the Georgia Secretary of State and candidate for governor, was the target of a credible written threat, his campaign said Tuesday.

Campaign spokesperson Ryan Mahoney said the threat came in the form of an apparent manifesto to a sheriff’s office in Mississippi that featured a photo of Raffensperger with the word “boom” scrawled across his face.

It was unclear if it was related to the discovery on Tuesday — a day after the campaign was notified about the written threat — of a suspicious object found inside a vending machine at a campaign stop in Macon that prompted the campaign to move the event outside.

The manifesto was not released and the motive was not publicly known, but the incidents are an apparent reminder of the potent threat of political violence in the U.S. especially for a high-profile candidate such as Raffensperger, who drew fierce criticism for resisting President Donald Trump’s efforts to resist the results of the 2020 election in Georgia.

“When you stand on principle, when you do the right thing, and when you put people ahead of politics, not everyone will like it. In fact, some people may try to intimidate or do you harm,” Raffensperger said in a statement posted to social media. “So yes, we are dealing with an active threat. And no, I will not back down.”

The Atlanta Journal Constitution first reported the written threat.

The suspicious object was detected by a law enforcement canine at the Middle Georgia Regional Airport where Raffensperger was set to hold a campaign event later in the day. The Bibb County Sheriff’s Department said in a news release later that there were no hazardous devices detected, but did not provide specifics of what was discovered.

The campaign went ahead with the scheduled event, opting to hold the gathering outside in the parking lot instead.

No arrests have been made.

Georgia State Patrol is leading the effort with support from the Georgia Bureau of Investigation and the FBI, Mahoney said, and the secretary will continue campaigning in the last week ahead of Georgia’s May 19 primary with heightened security.

“The secretary of state’s office has a law enforcement unit, so we’ll start traveling with a handful of those guys until the threat is alleviated,” Mahoney said.