(NewsNation) — A former Secret Service agent said he wasn’t “surprised at all” to learn that presidential candidate Robert F. Kennedy Jr. decided to cancel a campaign appearance in Des Moines, Iowa.

“On July 13 we saw for the first time in 43 years an actual attempt on a former president,” said Michael Matranga. “I believe that RFK Jr. and his campaign — as well as those that he’s working with within the Secret Service — are operating out of an abundance of caution.”

Trump sustained a flesh wound when a bullet grazed him during an attempted assassination in Butler, Pennsylvania, last month.

Kennedy canceled an Iowa State Fair appearance Thursday. His campaign cited “increased security concerns,” the Des Moines Register reported.

Kennedy was supposed to speak at 2:15 p.m. at the Des Moines Register’s Political Soapbox. His campaign said in a statement to NewsNation that they canceled Kennedy’s speech as they were “unable to secure a venue stage indoors to satisfy our security requirements.”

According to the newspaper, there were 10 people, including Kennedy, scheduled to speak at the Soapbox, an event that has attracted politicians from across the nation, and become a state tradition.

Trump has vowed to continue to hold outdoor rallies. Vice President Kamala Harris and running mate Tim Walz held a massive outdoor rally Wednesday in Eau Claire, Wisconsin. Matranga, however, said all situations are different — and present different challenges for security.

“I think the general public needs to understand that all of these sites are different, right? They’re different in scope. They’re different in size,” Matranga said. “They require different amounts of manpower and effort; none of them can be treated exactly the same.”