Donald Trump is ready to start the next nuclear arms race.

Set the “Days Without A Terrifying Donald Trump Tweet” meter back to zero. Late Thursday morning, Trump tweeted this:

There are two clues as to why Trump sent out such a reckless tweet. The first is that his good buddy Vladimir Putin recently announced that Russia wanted to update and expand its nuclear arsenal. The second is that Trump was reportedly briefed on nuclear weapons on Wednesday.

Countries update their nuclear arsenals, but they usually do so in careful ways. They are careful in the language that they use (Putin’s statement is cagey in this regard, at least compared to Trump’s) and careful in how and when they decide to announce such changes. And they’re careful for good reason: Just between the U.S. and Russia there are more than enough nuclear bombs to wipe out humanity. But Trump’s tweet doesn’t take any of this into account. Instead, he made a blanket statement that we need more nuclear weapons, without any context about what that would mean or how it would be accomplished. That statement alone will also tip off other countries with nuclear weapons (and, perhaps, those that would like some) that a new arms race is coming. And, to top it all off, the U.S. is already spending $1 trillion to “modernize” its nuclear weapons program—it’s unclear if Trump is even aware that’s happening.