Donald Trump often talks about trying to keep America’s adversaries scrambling to sort out his true intentions by being deliberately vague — and sometimes contradictory — in his public comments. His new call for the US to “expand its nuclear capability” has done that to his own aides as well.

Trump ignited his latest firestorm on Thursday, when he tweeted: "The United States must greatly strengthen and expand its nuclear capability until such time as the world comes to its senses regarding nukes."

The striking yet ambiguous comment was immediately interpreted as a sign that the Trump administration was willing to abandon decades of work by presidents of both parties — beginning with Ronald Reagan — to reduce America’s stockpile of nuclear weapons to lower the risk of a catastrophic conflict.

Trump’s aides immediately tried to offer a different — and, if true, far more reasonable — explanation. The president-elect, they said, wasn’t calling for the US to build more nuclear weapons; he was calling for renewed efforts to take better care of the ones the Pentagon already has. Trump spokesperson Jason Miller said the tweet was meant to emphasize the need to “improve and modernize our deterrent capabilities.”

But it didn’t take long for Trump to contradict his own aides. On Friday morning, Morning Joe host Mika Brzezinski said that the president-elect had actually meant what he first appeared to have meant. “Let it be an arms race,” she quoted him as saying to her and fellow host Joe Scarborough. “We will outmatch them at every pass and outlast them all.”

Trump regularly takes two positions on the same issue, often falsely insisting he didn’t say something he had publicly said or tweeted. That’s worrisome enough when it comes to denying that he’d called climate change a Chinese hoax when he’d literally said that exact thing. But it’s downright terrifying when it comes to nuclear weapons, which have the capacity to end human life.

So which one is it? Was Trump, in his own clumsy way, simply saying what other presidents have been saying for years about keeping America’s nuclear weapons in better shape? Or was he actually proposing that Washington start to build more of them?

We won’t know until he takes office, but it’s important to better understand just how different the two policies actually are — and that President Barack Obama, despite his dreams of a nuclear-free world, may already be in a new nuclear arms race with Russia and China.

America’s nuclear weapons are aging, and the troops guarding them may not be up to the job

In the spring and summer of 2014, dogged reporting by the Associated Press revealed a series of startling failures by US troops charged with maintaining some of America’s nuclear arsenal.

The first was that Air Force personnel at a base in Montana that stored nuclear-tipped intercontinental missiles had been routinely cheating on proficiency tests, meaning they might not have actually had the skills needed to keep the deadly weapons functioning safely. The commander of the base resigned, and nine others were fired for their role in the scandal, which implicated more than 100 officers.

The second, first reported by the AP, was that Air Force security personnel at Malmstrom had been unable to properly respond to a drill simulating the capture of a nuclear silo by a hostile force. An internal Air Force report said the security team’s inability to regain control of the silo quickly was “a critical deficiency.”

The gaffes at Malmstrom made headlines, but they were indicative of two lesser-known but far more dangerous facts: America’s nuclear arsenal is rapidly aging, with some missiles, submarines, and aircraft approaching obsolescence. And updating it will cost an enormous amount of money.

Obama, who took office dreaming of a world without nuclear weapons, has committed to spending at least $1 trillion over the next 30 years to modernize and upgrade that arsenal.

In part, his efforts reflect the urgent calls of top national security officials from both parties.

In 2008, then–Defense Secretary Robert Gates — a Republican who had served in the George W. Bush administration before later holding the same job during the Obama one — said the dire state of the US nuclear arsenal meant that it would be difficult to cut the numbers of nuclear weapons without potentially threatening American national security.

"To be blunt, there is absolutely no way we can maintain a credible deterrent and reduce the number of weapons in our stockpile without resorting to testing our stockpile or pursuing a modernization program," he said. "Currently, the United States is the only declared nuclear power that is neither modernizing its nuclear arsenal nor has the capability to produce a new nuclear warhead.”

But there’s second aspect of the Pentagon’s nuclear push: developing a new generation of nuclear weapons and the planes, missiles, and submarines that would carry them. That’s gained new urgency as Russia and China launch ambitious new nuclear weapons of their own. And that, in turn, is why Trump’s casual talk about a new arms race is so unsettling.

The foreign leader Trump most admires wants to have more nuclear weapons to aim at the US

On Thursday, just hours before Trump’s tweet, Russian leader Vladimir Putin issued his own call for expanding his country’s nuclear arsenal.

“We need to strengthen the military potential of strategic nuclear forces, especially with missile complexes that can reliably penetrate any existing and prospective missile defense systems,” he said.

He didn’t say whom those weapons would be aimed at, but he didn’t need to: As has been the case for decades, the Russian nuclear weapons were meant for potential use against the US and its NATO allies in Europe.

Pulling a page from the Trump playbook, Putin waited less than a day to insist that his seeming call for more nuclear weapons was actually just a call for making his country’s existing arsenal more effective in case of war. Russia, he said, “won’t start an arms race” with the US.

Despite the rhetoric, though, both Moscow and Beijing have been working hard in recent years to develop new and more advanced nuclear weapons. According to a long report in the New York Times, Russia is developing miniaturized nuclear warheads that would be easier to mount on long-range missiles as well as, potentially, an underwater drone designed to spread radioactive material over cities and make it unsafe for them to be lived in. China, meanwhile, is testing a new warhead called a “hypersonic glide vehicle” that can fly fast enough to evade most missile defenses.

Obama, wary of losing ground to the two American rivals, has signaled a willingness to spend roughly $1 trillion on the US arsenal over the next three decades.

Among the big-picture items: $100 billion for the Navy to build 12 new nuclear submarines; at least $55 billion (and likely far more) for the Air Force to build new nuclear stealth bombers; and tens of billions more on other Air Force efforts to build new nuclear cruise and ballistic missiles and modernize its B-61 nuclear bombs.

Obama has worked to ensure that the total size of the nuclear arsenal continues to fall, and that the US fully abides by existing nuclear arms control treaties with Russia. Putin has said he will do the same.

The grim reality, though, is that the nuclear dangers facing the world are already clearly on the rise. Trump may speed the arms race, but it began long before his election. That means even the most benign interpretation of Trump’s tweet should still be cause for deep, deep concern.