President Trump has called nuclear weapons "the single greatest problem the world has" – but he's also made some controversial statements about them. (Peter Stevenson/The Washington Post)

At the end of last year, after he won the election but before he was inaugurated, President-elect Donald Trump decided to proactively set U.S. nuclear policy via Twitter.

“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 Dec. 22. It was an out-of-the-blue declaration that made sense only as a response to a comment that Russian President Vladimir Putin had made earlier in the day, in which Putin suggested that his country planned to strengthen its own strategic nuclear arsenal.

In an interview with Reuters on Thursday, Trump revisited the issue, declaring that the United States has “fallen behind on nuclear weapon capacity.” He placed some of the blame for this on the 2010 New START agreement, a successor to the 1991 START agreement that was signed by President Barack Obama and aimed at further reducing the nuclear arsenals of Russia and the United States. New START, Trump said, was “another bad deal that the country made.”

“I am the first one that would like to see nobody have nukes,” he said, “but we’re never going to fall behind any country even if it’s a friendly country. We’re never going to fall behind on nuclear power.”

“If countries are going to have nukes, we’re going to be at the top of the pack,” he added.

During his daily news briefing, White House press secretary Sean Spicer was asked about the comments by Alexis Simendinger of RealClearPolitics.

“What he was very clear on is that the United States will not yield its supremacy in this area to anybody,” Spicer said. “That’s what he made very clear in there. And that if other countries have nuclear capabilities, it will always be the United States that has the supreme … supremacy and commitment to this.”

“Obviously, that’s not what we’re seeking to do,” he continued, apparently referring to expanding the nuclear arsenal. “The question that was asked was about other people growing their stockpiles. And I think what he has been clear on is that our goal is to make sure that we maintain America’s dominance around the world and that if other countries flout it, we don’t sit back and allow them to grow theirs.”

There’s a reason that the United States is cutting nuclear deals with Russia, of course: Only our two countries have nuclear arsenals of any significance. It’s a bit like Paul McCartney and John Lennon entering a music competition against two Nickelback cover bands and Jimmy Buffett. There are really only two people in the running.

While it’s impossible to know exactly how many nuclear weapons each nuclear nation has (such things are generally not public information), the Federation of American Scientists puts together estimates. Per its numbers, the United States has an arsenal of about 6,800 weapons to Russia’s 7,000 — with the next most heavily equipped nation being France at 300.

A lot of considerations come into play when assessing nuclear arsenals, including the nuclear triad, the tripartite delivery system the military relies on for delivery. The Obama administration had proposed modernizing the U.S. nuclear arsenal, including the triad, though it later sought to scale that back.

The position of the United States and Russia as defined in the New START agreement was that both nations desired to “forge a new strategic relationship based on mutual trust” and, therefore, work to “bring their respective nuclear postures into alignment with this new relationship” and “to reduce further the role and importance of nuclear weapons.”

It’s not clear where Trump sees a threat to our nuclear position, if not from Russia. It’s not as though North Korea’s nascent nuclear program is going to suddenly challenge our own, necessitating a quick ramp-up in developing intercontinental ballistic missiles. If Trump’s concerned about Russia having slightly more nuclear weapons than us, well, it has for some time.

According to the FAS, Russia (then the Soviet Union) had passed the United States in the size of its nuclear arsenal before Ronald Reagan took office.

Trump’s assertions in December and to Reuters fit with his broad policy toward military strength: peace through dominance. While Spicer is correct that this doesn’t necessarily mean an immediate buildup of nuclear capability, it continues to represent a break from Trump’s predecessors — and from the negotiated New START agreement, which remains in effect until February 2018.