What did Donald Trump do today?

He tweeted that the United States needed a bigger and more powerful nuclear arsenal, at least "until such time as the world comes to its senses regarding nukes."

The United States has about 1,900 nuclear weapons. There is no possible deterrent effect from more or bigger ones. Trump has struggled with the basic elements of nuclear strategy in the past.

Reducing an unnecessarily large and inherently dangerous stockpile has been an important goal for the US (and its adversaries) since the 1960s. Non-proliferation has been an even higher priority with respect to nuclear weapons for even longer.

The tweet outlining what may be a Trump nuclear doctrine was met with horror, with the notable exception of Vladimir Putin, who had made a similar call on Russia's behalf several hours earlier. 

Why is this so bad?

• Nuclear weapons policy should not be blurted out over Twitter.

• It's a bad sign if it's not clear where sudden changes like this are coming from.