On Thursday, Donald Trump tweeted that the United States should "greatly strengthen and expand its nuclear capability until such time as the world comes to its senses regarding nukes" -- a reversal of the long-term trend with nuclear weapons. In March, we explored his comments about nuclear proliferation and spoke to an expert who differentiated between upgrade our arsenal and expanding it. That article is below.

Say what you will about Donald Trump, but his pledge to Make America Great Again -- to make it great as it was under Ronald Reagan, as he has explained in the past -- is comprehensive.

Those of us old enough to remember the era will recall that the existential threat faced by the United States at that point was a nuclear war with the Soviet Union. Late in the second Reagan term, the world had more nuclear devices than ever before or since, as tallied by the Bulletin of the Atomic Scientists. We started with two devices in 1945, used both of those, and quickly built up an arsenal of tens of thousands — an arsenal matched by the Soviet Union. That knowledge then seeped out to other nations through innovation and espionage.

The data above end at 2010, the year the New START treaty further reducing stockpiles was ratified. Those reductions began in 2011.

The idea during the Cold War was that neither the United States nor the Soviet Union was likely to launch a nuclear strike against the other, knowing that its opponent had more than enough nuclear weapons to completely destroy it in return. The idea even had a name: "mutually assured destruction," or MAD. Whether or not this was the best strategy, both the United States and the USSR survived -- until the early 1990s, when the latter broke into a number of smaller countries.

In recent conversations with The Washington Post, the New York Times and, on Wednesday, with MSNBC, Trump has suggested that countries like South Korea and Japan should be empowered to have their own nuclear arsenals in order to protect themselves against North Korea.

"Biggest problem, to me, in the world, is nuclear, and proliferation," Trump said to the Times. "At the same time, you know, we’re a country that doesn’t have money." He later added: "[W]ould I rather have North Korea have them with Japan sitting there having them also? You may very well be better off if that's the case."

Trump has at times appeared to subscribe to Richard Nixon's "madman theory" -- that unpredictability in foreign relations is a virtue. Nixon wanted our opponents, including the North Vietnamese and the Soviets, to think that he might be crazy enough to use a nuclear strike as a form of forcing negotiations.

"When he refers to Nixon and says he wants all options on the table [and] he wants to be unpredictable -- that is extremely dangerous when it comes to nuclear security," Rachel Bronson of the Bulletin of Atomic Sciences said when we spoke by phone on Thursday. The Bulletin is the group that runs the famous Doomsday Clock, measuring how the world is moving toward or away from global catastrophe. This year, the clock remained at three minutes to midnight, a function of tensions between the two countries that make up most of the graph above.

"My concern and the concern about the way Donald Trump is talking about this," she said, "is that right now in terms of nuclear security and nuclear stability we are at a very unstable moment because of the deteriorated relationship between Russia and the United States." There are a lot of reasons for that relationship having frayed, on both sides. Part of the challenge is that efforts by the militaries of both countries to modernize their old nuclear stockpiles -- important from a safety standpoint -- also rebuilds infrastructure for those weapons to stick around for decades to come.

"We need to be very careful we don't kick off a new arms race, and we're on the cusp of doing that," Bronson said. "Just tripling down on the existing Cold War architecture and reinvesting in aspects of it is missing a huge opportunity to think about how we continue to reduce our stockpiles."

The White House also weighed in on Trump's statements about increasing the number of countries with nuclear weapons, which, obviously, would increase the number of situations in which they might be used. Such a proposal, deputy national security adviser Ben Rhodes said, would be "catastrophic."

On Wednesday, the president wrote an op-ed for The Post.

"I said in Prague that achieving the security and peace of a world without nuclear weapons will not happen quickly -- perhaps not in my lifetime," he wrote. "But we have begun. As the only nation ever to use nuclear weapons, the United States has a moral obligation to continue to lead the way in eliminating them."

The next president may disagree.

Here’s a look at Trump’s administration so far

Dr. Scott Gottlieb is seen in this American Enterprise Institute photo released in Washington, DC, U.S., March 10, 2017. Courtesy The American Enterprise Institute/Handout via REUTERS ATTENTION EDITORS - THIS IMAGE WAS PROVIDED BY A THIRD PARTY. EDITORIAL USE ONLY. NO RESALES. NO ARCHIVE. (Handout/Reuters)