President-elect Donald Trump raised the prospect of a new global arms race on Thursday, after he suggested on Twitter he would increase the size of the U.S. nuclear arsenal. Trump’s tweet read, “The United States must greatly strengthen and expand its nuclear capability until such time as the world comes to its senses regarding nukes.” At the State Department, the outgoing Obama administration spokesperson John Kirby was asked about the tweet.

John Kirby: “I can’t speak for the president-elect’s nuclear views or his policy going forward. That’s for him and his team to speak to. What I can speak to is the approach that this administration has taken to try to get us on on a path to a world without nuclear weapons.”

Despite President Obama’s call for an end to nuclear weapons, his administration has been quietly upgrading its nuclear arsenal to create smaller, more precise nuclear bombs as part of a massive effort that will cost up to $1 trillion over three decades. Speaking to MSNBC’s Rachel Maddow on Thursday, Trump’s former campaign manager, Kellyanne Conway, defended the president-elect’s tweet, pointing to President Obama’s nuclear plans.

Kellyanne Conway: “I don’t think the tweet was groundbreaking in this regard. It seems that President Obama himself has invested––has called for an upgrade in our capabilities. I’ve read in one or two articles, up to $1 trillion is the price tag. So, we all—you know, President Obama, President-elect Trump—everyone shares the same, I think, core value, and their first duty is to try to keep us all safe. And we know it’s a dangerous world, and that includes nuclear weapons.”

That was Trump’s former campaign manager, Kellyanne Conway, who Trump named yesterday as counselor to the president. This morning, MSNBC host Mika Brzezinski said she spoke briefly to the president-elect on the phone and asked him about his nuclear weapons comments. Brzezinski recounted Trump’s response during a conversation with co-host Joe Scarborough.

Joe Scarborough: “Mika asked the president-elect, while we had the opportunity, what his position was on—trying to clarify the tweet yesterday regarding the nuclear arsenal. And the president-elect told you what?”

Mika Brzezinski: “Let it be an arms race. We will outmatch them at every pass.”

Joe Scarborough: “And outlast them all.”

Mika Brzezinski: “And outlast them all.”

According to the International Campaign to Abolish Nuclear Weapons, about 93 percent of all nuclear warheads are owned by Russia and the United States, which together have about 14,000 warheads stockpiled.