WASHINGTON — President-elect Donald Trump Thursday decried the state of the nation’s nuclear arsenal, saying in a tweet that it had to be strengthened “greatly” during uncertain times.

“The United States must greatly strengthen and expand its nuclear capability until such time as the world comes to its senses regarding nukes,” he tweeted.

Trump made his remarks a day after receiving a national security briefing from a group of mostly senior military officers, including Air Force Lt. Gen. Jack Weinstein, deputy chief of staff for strategic deterrence and nuclear integration.

A nuclear arms reduction expert reacted to Trump's tweet with alarm. Joseph Cirincione, president of the Ploughshares Fund, said similar statements by Russian President Vladimir Putin could trigger a new and destabilizing nuclear arms race.

The United States and Russia have 95% of the world's nuclear weapons, but smaller nuclear powers, such as China, North Korea, India and Pakistan, may view their statements as a call to bolster their own arsenals, he said.

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"If the two guys with the biggest arsenals are talking about expanding, they're sending a message to the other guys that it's time to start their engines," Cirincione said. "And we’re off to the races."

An alternative, Cirincione suggested, would be for Trump and Putin to establish a relationship in which arms reduction is a centerpiece.

"He could assure his place his place in the history books with the deal of a lifetime," Cirincione said.

Later Thursday afternoon, Jason Miller, Trump's communications director, said Trump was referring to potential nuclear terrorism and other issues.

"President-elect Trump was referring to the threat of nuclear proliferation and the critical need to prevent it — particularly to and among terrorist organizations and unstable and rogue regimes," Miller said in a statement. "He has also emphasized the need to improve and modernize our deterrent capability as a vital way to pursue peace through strength.”

None of that was clear in Trump's initial tweet, and the president-elect did not speak publicly or send another tweet with more information.

What's a triad?

During the campaign for the Republican nomination and the general election, Trump struggled to show a firm grasp of U.S. nuclear strategy and capability.

In a Republican debate, Trump failed to define the “nuclear triad,” the U.S. nuclear strategy of relying on three weapons platforms to launch weapons — bombers, land-based missiles and submarine-launched missiles. The decades-long strategy is meant to deter enemies from attacking because they will be unable to prevent a devastating response.

Trump has also suggested that U.S. allies such as Japan, South Korea and Saudi Arabia, all of whom rely on the U.S. nuclear deterrent, could acquire nuclear weapons for their own defense.

The Pentagon, in its 2017, budget has several initiatives aimed at modernizing its nuclear arsenal. Among them is a $2.1 billion program to develop a new, radar-evading long-range bomber.

Pentagon records show that between 2017 and 2021, the Defense Department "anticipates spending approximately $100 billion on both sustaining and modernizing our nuclear forces, including nuclear command and control." About $34 billion will be spent on replacing aging submarine-based weapons, "ICBMs, heavy bombers, dual-capable fighter-bombers in NATO, as well as our air launched cruise missile and gravity bombs."

Robert Jervis, professor of international affairs at Columbia University and an expert on nuclear weapons, downplayed the notion that Trump’s tweet would set off a new arms race. More troubling, he said, is that there’s no evidence that Trump has thought long or hard about the policies for maintain and using them.

Does he want to spend more than the $350 billion the Obama administration has proposed to modernize them, Jervis asked? What happens if Putin rejects his offers for better relations? The problems are complex, and the stakes exceedingly high, he said.

“Unless we’re being fooled and he’s done great thinking, these tweets are off the top of his head and are immediate responses,” said Jervis, who acknowledged being a lifelong Democrat. “If you try to dig deep there isn’t anything there. There’s a reason states don’t communicate in 140 characters without serious staff work.”

Defense Secretary Ash Carter recently commented on the need to modernize nuclear weapons while at a base in North Dakota.

"If we don't replace these systems, quite simply they will age even more, and become unsafe, unreliable, and ineffective," Carter said. "The fact is, most of our nuclear weapon delivery systems have already been extended decades beyond their original expected service lives. So it's not a choice between replacing these platforms or keeping them; it's really a choice between replacing them or losing them."

The world has seen a dramatic reduction in the number of nuclear weapons in the last 25 years, Pentagon records show.

Dec. 12 was the 25th anniversary of the Soviet Nuclear Threat Reduction Act of 1991 Since then, Pentagon statistics show, more than 7,600 nuclear warheads have been deactivated, while the United States, Russia and former Soviet republics have destroyed more than 3,600 missiles and missile launchers, 33 submarines, 155 bombers, more than 1.6 million chemical munitions, and more than 4,000 metric tons of chemical weapons.

Contributing: Jim Michaels and David Jackson

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