(CNN) 鈥 When Chinese leader Xi Jinping inserted a reference to 鈥渢wists and turns鈥 in his relationship with in the opening remarks of their summit this week, he could hardly have imagined the twist that came minutes before the talks began.
Writing from Marine One, which was gliding toward the airport in South Korea where he was due to meet Xi, Trump to resume nuclear testing after a 33-year pause, citing other nations鈥 鈥 including China鈥檚 鈥 own capabilities.
鈥淭hat process will begin immediately,鈥 the president wrote on social media.
The directive took even many of Trump鈥檚 advisers off guard, according to officials, leading to unanswered questions about when, or if, the testing would actually begin. Historically, it is the Department of Energy that maintains and tests the US nuclear stockpile, not the Department of Defense. And engineers have said accurate tests can be conducted through computer simulation, not blowing up an actual warhead underwater or in the Nevada desert.
Hours after the president鈥檚 post, it did not appear as if the Pentagon was moving swiftly to test a nuclear weapon. Testifying on Capitol Hill, the senior military officer nominated to oversee the American nuclear arsenal said Thursday morning he was not 鈥渞eading anything鈥 into Trump鈥檚 Truth Social post 鈥 an indication, if one was needed, that the instructions hadn鈥檛 been previewed very widely ahead of time.
The surprise message only underscored the volatile approach Trump is taking to foreign affairs nine months into his second administration. Even as he was about to sit down for a meeting intended to lend stability to the world鈥檚 most important bilateral relationship, Trump demonstrated his willingness to suddenly veer in an unexpected direction.
Administration officials offered little clarity when questioned about the message on Thursday.
鈥淚 think the president鈥檚 Truth speaks for itself,鈥 Vice President JD Vance said as he took questions from reporters at the White House. 鈥淲e have a big arsenal. Obviously, the Russians have a large nuclear arsenal. The Chinese have a large nuclear arsenal. Sometimes you鈥檝e got to test it to make sure that it鈥檚 functioning and working properly.鈥
鈥淭o be clear, we know that it does work properly,鈥 he added later, 鈥渂ut you got to keep on top of it over time, and the president just wants to make sure that we do that.鈥
When asked by reporters in Malaysia on Friday about Trump鈥檚 post, Defense Secretary Pete Hegseth said the Pentagon would move quickly and work with the Department of Energy. He argued that 鈥渞esuming testing is a pretty responsible鈥 way to keep a 鈥渃redible nuclear deterrent.鈥
Dating back to his first term, Trump has always maintained a somewhat complicated relationship to the nuclear weapons he can launch from a secure suitcase anywhere he goes.
A product of the nuclear era, he recently voiced wariness at even mentioning the word itself: 鈥淲e can鈥檛 let people throw around that word,鈥 the president told generals last month. 鈥淚 call it the n-word. There are two n-words, and you can鈥檛 use either of them.鈥
He seemed less cautious in his this week.
鈥淭he United States has more Nuclear Weapons than any other country,鈥 he wrote. 鈥淭his was accomplished, including a complete update and renovation of existing weapons, during my First Term in office. Because of the tremendous destructive power, I HATED to do it, but had no choice!鈥
Afterwards, Trump was circumspect about what tests, precisely, he was asking for.
鈥淲ith others doing testing, I think it鈥檚 appropriate that we do also,鈥 Trump said aboard Air Force One as he was returning to Washington.
He said nuclear test sites would be determined later, and specified his message did not relate to China 鈥 even though he named the country specifically in his message. 鈥淚t had to do with others,鈥 he said vaguely.
Some officials said Trump may have been prompted by Moscow鈥檚 test flights in recent days of nuclear-capable cruise missiles and torpedoes, though their existence was already known and the tests did not involve a nuclear detonation. There is also no US equivalent to those Russian systems that could be tested to demonstrate equivalence, because the US decided decades ago that developing those systems was unproductive, said a former Trump administration official who worked on nuclear issues.
Neither China nor Russia have conducted a nuclear test in decades. While China has worked rapidly to expand its arsenal, it is not known to have conducted an explosive test since 1996.
Beijing鈥檚 speedy buildup in nuclear weapons has nonetheless generated concern among administration officials, who regard the issue as yet another point of friction in an increasingly tense relationship. Xi presided over a flashy parade of China鈥檚 nuclear-capable missiles last month.
鈥淩ussia has nearly completed their modernization of all of their nuclear forces, and China is modernizing, and they are growing their arsenal at a breathtaking speed,鈥 Elbridge Colby, the US undersecretary of defense for policy, said during his confirmation hearing this year.
Still, if Trump was ordering up the first test of a US nuclear explosive since 1992, it came as news to the military officer he nominated to oversee the nation鈥檚 vast arsenal of nuclear weapons.
鈥淚 wouldn鈥檛 presume that the president鈥檚 words meant nuclear testing,鈥 Vice Adm. Richard Correll, whom Trump tapped to head up US Strategic Command, said before the Senate Armed Services Committee on Thursday.
鈥淚 believe the quote was, 鈥榮tart testing our nuclear weapons on an equal basis,鈥欌 Correll went on. 鈥淣either China or Russia has conducted a nuclear explosive test, so I鈥檓 not reading anything into it or reading anything out to it.鈥
If confirmed to the position, Correll would be responsible for the more than 41,000 service members who look after components of the US nuclear weapons program, including submarines, ballistic missiles and Air Force bomber aircraft. He has served as the deputy commander of US Strategic Command since 2022 鈥 so it鈥檇 be unusual if he didn鈥檛 know know about a change in the decadeslong moratorium on nuclear testing.
The Trump administration has not changed the nuclear modernization policy that was put into place during the final year of the Biden administration, with the aim of pivoting the strategic plan to deter China鈥檚 nuclear buildup. But carrying out a nuclear test could set back that modernization strategy because it would reorient the focus of the officials working on those ongoing efforts, according to former US officials who worked on nuclear issues.
There are also concerns among those officials that Trump declaring the intent for US nuclear testing would actually benefit China 鈥 not the US.
鈥淭he mere suggestion that the US may resume nuclear testing could give the green light to China to resume explosive testing, and the Chinese would benefit comparatively more than anyone else if testing resumed. There is no technical reason for the US to do this now. But for China, it could technically advance their capabilities,鈥 a former senior US official said.
Yet Trump has long approached nuclear weapons with a combination of morbid fascination and bombastic threats.
In August, he announced he was ordering two nuclear submarines to be strategically positioned near Russia in response to what he said were aggressive remarks by Dmitry Medvedev, the country鈥檚 former president and current deputy chairman of its Security Council. He never clarified whether he was referring to subs with nuclear weapon capabilities, or merely nuclear-powered subs.
In a particularly heated moment from his first term, Trump taunted North Korea鈥檚 Kim Jong Un 鈥 whose 2017 underground test is the last known example of explosive nuclear testing 鈥 for the relative size of his 鈥渘uclear button.鈥
鈥淚 too have a Nuclear Button, but it is a much bigger & more powerful one than his, and my Button works!鈥 Trump wrote on social media in 2018.
He and Kim eventually improved relations and met in person three times 鈥 though Trump was never able to convince the despot to abandon his nuclear weapons.
Now, Trump appears hopeful to begin tests quickly 鈥 though just how quickly may depend on his willingness to break international rules.
鈥淚f the United States needed to conduct an immediate nuclear test to, say, verify that some of its weapons were working or for political purposes, it could violate a whole number of treaties that ban doing that in the atmosphere. And that could happen in a matter of weeks or maybe months,鈥 said Jon Wolfsthal, a former senior director for arms control and nonproliferation at the National Security Council, who now is director of global risk at the Federation of American Scientists.
鈥淭he United States has a test site just outside Nevada where we conducted these tests in the 1990s and before,鈥 he added.
鈥淏ut it鈥檚 not poised to conduct testing anytime soon, and it takes years to scientifically instrument a test to make sure you鈥檙e getting the data out of it that you need. And I also assume that states like Nevada and others would sue to block the president鈥檚 ability to do this. So we鈥檙e several years away from being able to conduct explosive nuclear tests.鈥
This story has been updated with additional information.
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