Retired Marine general James Mattis during a meeting with Senate Majority Leader Mitch McConnell on Dec. 7. (Alex Wong/Getty Images)

President-elect Donald Trump has called for the United States to “greatly strengthen and expand” its nuclear capability, but his nominee to run the Pentagon has suggested it is time to question whether the United States still needs so many nuclear weapons and three separate ways to deliver them.

Retired general James N. Mattis, testifying as a national security expert before the Senate Armed Services Committee last year, said the United States must “clearly establish the role” of nuclear weapons in U.S. policy.

“Do they serve solely to deter nuclear war?” the retired four-star Marine said. “If so, we should say so, and the resulting clarity will help to determine the number we need.”

Currently, U.S. nuclear policy leaves open the door to nuclear weapons being used in response to some conventional or chemical attacks. But if their function were narrowed further — to only deterring nuclear war — that might lead to the country continuing to scale down its arsenal of 4,500 warheads. Recent efforts to reduce nuclear stockpiles worldwide have stalled in part due to chilly U.S. relations with Russia.

Mattis added that it was time to ask whether it was “time to reduce the triad to a dyad,” a reference to the long-running debate about whether the United States must continue to keep and maintain its decades-old arsenal of intercontinental ballistic missiles (ICBMs). Doing so, Mattis said, could reduce the “false alarm danger,” in which a nuclear war is set off by mistake. Currently, the Pentagon can launch nuclear attacks using ICBMs, missiles launched from submarines and ordnance dropped by bombers.

Trump tweeted Thursday that the United States “must greatly strengthen and expand its nuclear capability until such as the world comes to its senses regarding nukes.” The message was posted after Russian President Vladimir Putin said Moscow needs to “strengthen the military potential of strategic nuclear forces,” developing arms that can avoid missile defense systems.

On Wednesday, Trump also met with Lt. Gen. Stephen W. Wilson, the vice chief of staff for the Air Force, and Lt. Gen. Jack Weinstein, the service’s deputy chief of staff for strategic deterrence and nuclear integration, both of whom have worked with nuclear weapons for years.

Jason Miller, a spokesman for Trump’s transition team, issued a statement Thursday afternoon that attempted to clarify the president-elect’s tweet. Miller said in an email to The Washington Post that Trump was referring to “the threat of nuclear proliferation and the critical need to prevent it” and was emphasizing “the need to improve and modernize our deterrent capability as a vital way to pursue peace through strength.”

That left open the possibility that Trump misspoke about his desire to “expand” U.S. nuclear capability rather than “modernize” it, but MSNBC reported Friday morning that Trump doubled down on the remark, saying “let it be an arms race” in a phone interview.

“We will outmatch them at every pass,” Trump said, according to MSNBC.

Sean Spicer, just named as Trump’s White House press secretary, disputed that there will be an arms race in a television interview afterward, saying Trump meant that he won’t allow other countries to expand their nuclear capabilities.

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)

Trump’s actual plans for nuclear policy remains unclear, but the generals he met with Wednesday have advocated keeping all three legs of the nuclear triad and upgrading the means of delivering nuclear weapons, noting that the “dual-capable” bombers also can deter enemies by dropping conventional bombs. They also often suggest that the continued existence of nuclear weapons has prevented massive state-on-state wars like World War II that can kill millions of people.

“Let me clear: Any death in war is a tragedy. One person dying is someone’s spouse, someone’s brother, a mother losing her child,” Weinstein said during an Air Force Association luncheon in August. “So, any death in war is tragedy. But world powers are not fighting world powers, and I believe that it’s because of a nuclear umbrella that exists and this balance of power that exists between major nations that have nuclear weapons.”

Defense Secretary Ashton B. Carter, the outgoing defense secretary, has advocated a similar stance, even while noting that it could cost $350 billion t0 $450 billion to modernize the Pentagon’s ability to deliver nuclear weapons by submarine, bomber and ICBM. In a speech at Minot Air Force Base, N.D., in September, he argued that if all three systems are not replaced, they will become unreliable and ineffective.

“It’s not a choice between replacing these platforms or keeping them,” Carter said. “It’s really a choice between replacing them or losing them. That would mean losing confidence in our ability to deter, which we can’t afford in today’s volatile security environment.”

Other senior officials, including former defense secretary William Perry, have called for a complete phasing out of ICBMs. Doing so, they argue, will remove a significant burden on defense budgets and boost the ability to upgrade other parts of the military.

Related stories:
Trump and Putin agree: Let’s revive the nuclear arms race

Five myths about nuclear weapons

Trump’s latest comments stoke talks of a nuclear arms race