Donald Trump tweeted something controversial today. After Twitter controversies involving Boeing, terror attacks, and former President Bill Clinton, Trump has directed his attention towards the American nuclear arsenal.  Thursday morning, Trump tweeted that “The United States must greatly strengthen and expand its nuclear capability until such time as the world comes to its senses regarding nukes.” The impetus behind the tweet is unknown, but Trump may have been responding to the concerns of Boeing and Lockheed Martin executives after a Wednesday meeting, or to a rather similarly-worded statement from Russian President Vladimir Putin early Thursday.

The idea and language in Trump’s tweet were hardly unprecedented, given his own history of statements on nuclear weapons, but concerns that a president or president-elect of the United States might spark an arms race or worse with Russia via Twitter are novel at least, and have real basis in his lack of an online filter. And his statements do go against the traditional public positions of recent American presidents on nuclear weapons that tend to display an eagerness to not use nukes, regardless of the policies actually being championed.

But does Trump’s tweet about nuclear weapons offer real cause for concern? I talked to Jeffrey Lewis, adjunct professor at the James Martin Center for Nonproliferation Studies, about Trump’s tweets and nukes. The following conversation has been lightly edited for clarity.

Vann R. Newkirk II: What should people take from Trump's tweet today?

Jeffrey Lewis: The first thing is it's really hard to draw firm conclusions from a tweet, which seems like an obvious thing to say, but presidential utterances have a kind of importance that is hard to square with the brevity of a tweet, so we're in a weird position. At some level it's pretty unremarkable. President Obama was fond of saying that as long as nuclear weapons exist, we'll maintain a safe, secure, and effective arsenal. The sentiment isn't really different than him saying we should make our nuclear weapons better until other people come to their senses. It's classically Trumpian in that he says what other people say, but finds a way to say it that's boastful and inflammatory. But the sentiment beneath it isn't radically different.

Newkirk: So that rhetoric doesn't entail substantial changes from existing policy?

Lewis: I don't think so. There's been a certain continuity in the way our nuclear policy has looked over the past 30 to 40 years, and there's a reason for that. There are all these structural factors that are a lot harder to overcome. It's easier to tweet a policy change; it's a lot harder to implement it. The Obama administration agreed to a pretty substantial modernization program, and the constraints on that modernization program are: Do we have enough money? Do we have enough capacity to execute it? Will the programs be delivered on time? Will they work? So Trump can tweet about making things better all he wants, but that doesn't actually deliver on those promises. So my suspicion is the tweet is basically cheerleading. It doesn't materially affect the outcome of the game.

Newkirk: What does modernization even mean in the context of a nuclear arsenal?

Lewis: Well, it doesn't mean anything. These words are shorthand for really complex things. In some cases it means taking existing systems and extending their service life. In other cases it means replacing existing systems with new things. So we're building new bombers and new submarines and there are plans to build a new ICBM, and the warheads are being refurbished. At the beginning of the Obama administration, there was a big argument about whether to use the word 'modernization.' The hawks wanted to call it modernization. And the doves wanted to not call it modernization because that sounds like we love nuclear weapons. But there wasn't all that much dispute about the underlying programs. It was just really what you called them. So I think that was kind of the message of the tweet too, is Trump is enthusiastic about saying we're making the arsenal better, but I don't think that will necessarily translate into policy choices.

Newkirk: With so much power in our and Russia's arsenals, why does this always take the shape of a race?

Lewis: Well, like all popular metaphors, it's at once appealing and deeply wrong. I think that men like to compare their penises, and 'race' is the slightly better metaphor. In the 70s, Paul Warnke, who was eventually Jimmy Carter's choice for Director of the Arms Control and Disarmament Agency, wrote an article in which he compares that U.S.-Soviet arms race to two joggers on a treadmill. In that article he has a famous quote that says "We can be first off the treadmill. That's the only victory the arms race has to offer."

Newkirk: We might not want to read too much into this tweet, but with nuclear rhetoric between the two state leaders, how much concern should we have about how that rhetoric shapes policy?

Lewis: Well, I'm worried about it. But there's good news and bad news. The bad news is the Russians seem to be investing very heavily in a range of new capabilities and I worry that their numbers will stop coming down and start going up, and the president-elect seems to be very enthusiastic about running that arms race with the Russians. The idea that numbers could start to increase is worrisome. The good news is—and I admit it's not all that great of news—listening to Trump and Putin talk about their nuclear arsenals is less ideological rivalry from the Cold War and more like two guys at a Camaro meet-up. They're both in love with their toys, and they love showing them off, and I think they get some kind of charge out of them. But it isn't clear to me that it's linked to any kind of geopolitical worldview. It's just an adolescent enthusiasm for bigger and better toys.