ASPEN, Colo. — Mark Esper, a former secretary of defense during the Trump administration, said on Wednesday that the administration needs to be more proactive in responding to assassination attempts by the Iranian regime targeting former President Donald Trump, other members of his administration and Iranian dissidents.

Reports emerged this week that, separate from the apparent lone-wolf assassination attempt at a Trump campaign rally last weekend, the former president is also being targeted by Iran. Esper himself continues to have a security detail due to Iranian threats on him, retaliation for the killing of Gen. Qassem Soleimani.

“We’ve got to do better than just playing defense,” Esper said at the Aspen Security Forum. “Just sitting back playing defense and waiting for them to get lucky or not get lucky, to me, is not a winning strategy, not least because of our own personal livelihoods, and what that may mean to our welfare.”

He argued that any attempt on the life of the former president should be considered an act of war, and that even the act of planning it could be considered an act of war.

Esper said that the administration should be tracking down the Iranians responsible for planning the attacks and hitting back through either legal or military means, “until the Iranians get the point and understand that they need to knock this off.”

Esper added that there’s currently uncertainty around Iran’s next steps, explaining that it remains unclear how the new Iranian president, Masoud Pezeshkian, will shape the country’s foreign policy and malign activities, nor what the succession process will look like for Supreme Leader Ayatollah Ali Khameini.

The former defense secretary said he was “surprised” by the scope of the Iranian attack on Israel in April, when hundreds of missiles and drones were fired at the Jewish state. Esper described the attack as “a very bold move that really could have drawn the Middle East in a much bigger conflict, to include us,” showing, “a new level of derring-do on their behalf.”

He said that the largely failed Iranian attack, and the Israeli counterattack, had also exposed weaknesses in Iran’s military and defenses.

Esper said that he agrees with assessments that Hamas cannot be eliminated fully through military means, given that “it’s an ideology, it’s a cult, it’s a movement,” but that some elements of the threat can be tackled through military means, including dismantling tunnels, eliminating the fighting capacity of its current brigades, killing top leaders and securing the corridor between Egypt and Israel.

“What you’re gonna have to do is have a presence there, or at least the means to — as we like to say colloquially — ‘mow the grass’ every now and then,” Esper said. “You go in, you take them out, you do these types of things, but you actually have to get a new administering authority there on the ground to do the police, the education, the governance, all those things that a normal state would do. And having it run by a terrorist organization is not a way forward.”

Esper and Jeh Johnson, a former secretary of Homeland Security during the Obama administration, also discussed the attempted assassination attempt on Trump.

Johnson said that it remains unclear what went wrong in security protocols. He noted that the Secret Service agents have been successful for 43 years in preventing an attempted shooting of a current or past president, or presidential candidate, but that there was “obviously a failure of communication” over the weekend.

“I don’t know what level of heightened security there was around him because of these reports about threats from the Iranians,” Johnson said. “I’m sure that’ll come out, but their major hard questions have to be asked.”

Both Esper and Johnson said they were concerned by the finger-pointing and shifting explanations provided by the Secret Service and local law enforcement in response to Saturday’s attack.

“You do want to be transparent, but you’ve got to be careful that you’re not feeding the bigger beast, because now it looks like we’re hopping from excuse to excuse,” Esper said. “And I know that’s not the intent, because the Secret Service is extremely professional, but it just kind of feeds into this broader turmoil of each side blaming and saying, ‘This happened. This didn’t happen, and it’s a cover up, and the director should be fired or not fired.’”

Esper and Johnson said that political leaders, elected and non-elected, have a responsibility to calm tensions and rein in political rhetoric. Johnson also lamented the prevalence and accessibility of high-powered guns like the one used by the shooter.

Speaking on another panel earlier in the day, Matthew Noyes, the director of cyber policy and strategy at the U.S. Secret Service’s Office of Investigations, said the Secret Service has long been “constrained” by budget limits, impacting his staffing and resources.

Johnson similarly warned of the Secret Service’s under-resourcing, noting that expanded protection requirements require it to pull staff from its financial investigations arm.

Speaking alongside Noyes, Brian Nelson, the undersecretary of the Treasury for terrorism and financial intelligence, said that lone-wolf attacks, like the attempted assassinations, are difficult to track or predict through financial channels.

“In this case, we’re working very closely with the FBI on their investigation, and continue to do so, but this is an area where, frankly, we have really struggled to send clear guidance to financial institutions,” Nelson said.