If President Trump's planned meeting with Kim Jong Un happens, those planning security for the event can't deny the dictator's past, which include allegations that he ordered his brother's death at a public airport when a pair of women splashed his face with precursors of the VX nerve agent.

Trump’s summit with the young dictator is tentatively planned for sometime before May and has many unresolved details, including the location and date.

Experts know that a diplomatic meeting between Trump and Kim would be tightly controlled, with negotiations between U.S. and North Korea determining the number of security personnel joining each leader, as well as any accompanying weaponry.

But there are significant unknowns, including whether Kim would be physically searched, and whether the choice of venue would make it difficult to protect against the most extreme scenarios involving physical risk to Trump.

Experts familiar with diplomatic and security processes cite North Korean self-interest as the best defense against a jarring assault during the meeting, though many note it's difficult to predict the behavior of one of the world's most closed, repressive nations.

An assault on Trump would be an unlikely twist to an apparent opening for rapprochement, but North Korea has a long history of assassination schemes against dissidents and rivals. And experts say no level of security can be foolproof.

“There’s no way to guarantee security. If Kim wants to detonate a tactical nuke, there’s really nothing the Secret Service or anyone else is going to do,” said Dan Bongino, a former Secret Service agent who worked five years on the presidential protection detail, leaving in 2011.

Bongino believes, however, that security agents likely would be able to detect common unseen threats from nuclear, biological or chemical contaminants at the venue.

The former agent declined to discuss the specific technical detection tools available during his time with the agency, but said he's confident that the latest available machinery would be used by specialists whose training narrowly focuses on specific risks.

The Secret Service "has the best detection systems in the world [and] works in conjunction with the military and obviously without giving away secrets, they have very specialized units," Bongino said. “There’s detectors and plans for everything: radiation, hazardous chemicals, nerve agents, biological agents.”

“I promise you the president is not going anywhere where a deadly nerve, chemical or radiological agent is present," he said. “I’ve done multiple foreign advances where I was the lead, and nobody does it like they do it. It’s the model for success. There’s no room for failure; they think of things so bizarre you’d probably laugh.”

Still, in an era where the creative science of assassination is honed with brazen public assaults, such as the airport killing of Kim Jong Nam in Malaysia, can Trump truly be safe, either from unseen contaminants or a more conventional attack?

John Parachini, who oversees the Rand Corporation’s support for the U.S. intelligence community as director of the think tank’s Cyber and Intelligence Policy Center, said “the chance is not zero, but it’s not high, either” of a potential assault.

“Can you provide perfect protection? No," he said.

Parachini, who researches weapons of mass destruction, bases his assessment on logic.

“Killing a head of state, particularly of a superpower” would be “national suicide” for North Korea, Parachini said, a risk that “even someone like Kim Jong Un, who seems as volatile as the president in certain respects” would not take.

“Where the meeting site is bears importantly” on the level of security that can be provided, Parachini said, with a North Korean location near impossible to secure, and options in China or along the Demilitarized Zone easier to safeguard, albeit imperfectly.

The science of detecting unseen lethal threats is hardly straight-forward. Dr. Howard Hu, a professor at the University of Toronto who has studied post-exposure examples of chemical weapon use, including against Iraqi Kurds in the late 1980s, said he would expect a meeting to occur in a neutral and “extremely well-resourced and prepared” country that can provide security, but that “even then, there will obviously need to be a leap of faith.””

With the possible U.S.-North Korea summit, one major unknown involves whether Kim would be searched by the Secret Service, and whether there would be a handshake or an avoidance of physical contact with a polite bow.

“No question the Secret Service will require that Kim submit to a search and screening for chemical, biological, or radiological weapons,” said journalist and author Ronald Kessler, an expert on the Secret Service who exposed security lapses involving prostitutes in Colombia during a 2012 visit by President Barack Obama.

“This is an unprecedented situation where a U.S. president is meeting with the leader of a murderous rogue regime in an age when WMD[s] are highly developed,” said Kessler, who closely researched presidential protection for the books The First Family Detail and In the President's Secret Service .

Bongino, the former Secret Service agent, said he doubts Kim would be searched, however.

“I can't speak in categoricals, but I see that as highly, highly unlikely. You’re not searching our guy under any circumstances … and the way these things work is usually quid pro quo,” he said.

Despite the risks involved, experts lean toward a belief the event can happen without unacceptable risks to Trump's safety.

Bonnie Jenkins, who held the rank of ambassador as the State Department’s Coordinator for Threat Reduction Programs between 2009 and 2017, focused largely on nuclear, chemical, and infectious disease threats, said she’s confident that the meeting can be held with an acceptable degree of risk.

“I am not an expert on field-testing techniques,” she said. “However, I am confident that the U.S. will be taking all necessary precautions to protect the president in this and in all cases where he is going to engage with foreign leaders. I would not say that anything is foolproof, but like I said, I do feel confident about any protection provided.”