President Donald Trump has suggested he has left standing orders for the US military to launch an unprecedented response if Iran follows through on its long-standing threats to assassinate him.
However, the US government has no legal mechanism for an automatic, pre-authorised "dead man's switch" that would trigger immediate military retaliation.
Instead, if a US president were assassinated, power would pass instantly to the vice president under the 25th Amendment and the Presidential Succession Act of 1947. Vice President JD Vance would become commander-in-chief and would decide whether and how to respond.
Under such circumstances, Vance could carry out the retaliation Trump envisaged, but he would not be legally bound to follow any standing orders and could choose a different course of action.
"The US has, for a whole variety of reasons, never utilised a technical 'dead man's switch'," said Garrett M. Graff, author of Raven Rock: The Story of the U.S. Government's Secret Plan to Save Itself -- While the Rest of Us Die.
While the United States maintains extensive continuity-of-government plans for a nuclear attack or other catastrophic events, those procedures do not provide for automatic retaliatory strikes following a president's death, even if such instructions had been issued in advance.
Trump wrote on his social media platform on Saturday that Iran had threatened "to assassinate, or attempt to assassinate" him, adding that 1,000 "missiles are locked and loaded and aimed at the Islamic Republic of Iran, with thousands more to immediately follow, should the Iranian Government act on its threat".
Hours later, Iran's Supreme Leader Mojtaba Khamenei said Iranians would continue to seek revenge for the killing of his father, Ayatollah Ali Khamenei, who died in the opening US and Israeli strikes that began the war in late February.
"We pledge to take revenge for your pure blood and the blood of all the martyrs of these two wars from the criminal and disgraceful killers," he said in remarks broadcast on state television. "This revenge is the will of our nation and must certainly be carried out."
The White House did not immediately respond to questions on Saturday about what would happen to Trump's reported military orders if he were killed.
During funeral processions for the elder Khamenei this week, mourners carried posters and banners calling for the deaths of Trump and Israeli Prime Minister Benjamin Netanyahu.
The Wall Street Journal reported this week that Israel had alerted US officials to fresh Iranian plots to assassinate Trump. While the White House declined to comment, Trump appeared to refer to such threats during this week's NATO summit in Turkey, saying: "They want to take out the US leader — me."
Sabrina Singh, a former deputy Pentagon press secretary under President Joe Biden, said Iran's interest in targeting senior American officials was well known.
"You have to take these as credible threats," she said.
Trump survived two assassination attempts during the 2024 presidential campaign and also faced another security scare in April when an armed man breached the White House Correspondents' Association dinner he was attending.
The president also flew part of the journey back from Turkey this week aboard an older Air Force One aircraft instead of a newly acquired Qatari-gifted jet, prompting fresh questions about the newer aircraft's defensive capabilities.
The change came as the United States and Iran resumed exchanging military strikes, threatening last month's agreement aimed at ending the war.
Asked about Iranian threats while aboard Air Force One, Trump said: "I'm No. 1 on their list."
Graff said the United States had long prepared for scenarios in which nuclear launch authority would need to pass quickly to another official following a surprise attack.
"What I believe Trump is saying is that he's left standing orders to attack if he's killed, for example, that the Pentagon should proceed with standard launch protocols," Graff said.
"There's a lot of reason to doubt the legality of such standing orders, since in the event of a president's death, the nuclear launch authority would immediately pass to the vice president or designated successor. Ultimately, it would be up to him or her to determine whether to proceed."
Trump's social media post referred only to missile strikes against Iran and did not mention the use of nuclear weapons.
Graff said Trump could also privately instruct Vance to launch a nuclear strike if he were assassinated, adding that such a directive "would make more sense and would be absolutely legal", although the final decision would still rest with the new commander-in-chief.
Warnings to Iran over alleged plots against Trump are not new.
In 2022, the Biden administration warned Tehran against targeting US citizens after the Justice Department disclosed an alleged plot by a member of Iran's Islamic Revolutionary Guard Corps to assassinate John Bolton, who served as Trump's national security adviser during his first term.
Then-national security adviser Jake Sullivan warned that "should Iran attack any of our citizens, to include those who continue to serve the United States or those who formerly served, Iran will face severe consequences."
Two years later, during Trump's presidential campaign against Democrat Kamala Harris, the Biden administration reportedly delivered another warning to Tehran, making clear that any attack on Trump would be treated as an act of war.