What did Donald Trump do today?

He threatened to bomb Oman, which he did not appear to understand is an ally in his war on Iran.

Oman is a de facto military ally of the United States. Nominally neutral in Trump's war on Iran, it has been negotiating in parallel with the United States to convince Iran to reopen the Strait of Hormuz. Iran has launched missile and drone attacks at Omani targets as a result of that relationship, but it's also offered to acknowledge joint sovereignty over the strait with Oman, which forms the southern shore of it.

Speaking to Fox News reporters today, Trump said that if Oman's negotiation "gets in the way, we'll bomb the shit out of them."

Oman is home to four airbases currently serving the US Air Force, and two critical naval bases used to supply and support US Navy ships operating in the region. In other words, Trump is not only threatening to bomb an ally actively involved in trying to provide him an escape from his war on Iran, but one that could easily attack US aircraft on the ground if provoked. Or—perhaps more immediately threatening to Trump—one of his luxury golf resorts.

Nothing in Trump's remarks to the reporters on the call indicated that he was aware of any of that.

Even by Trump's standards, this was a bizarre outburst. He's attempted to switch sides in the middle of a war: first with the Ukraine-Russia conflict, and more recently with his attempts to at least move towards neutrality between North Korea and South Korea. He's betrayed forces loyal to the US in Afghanistan and Syria, to the horror of American servicemembers who fought alongside them. And he's rattled his saber at NATO, less to promise an attack than to blow up the whole alliance—although he's refused to rule out an attack on Greenland. 

But this is the first time he's threatened to switch sides in a war the United States was actively fighting. As a near-infallible rule, nations simply don't do this, for obvious reasons. The closest historical parallel may be to Nazi Germany breaking the Molotov–Ribbentrop Pact and attacking the Soviet Union in 1941. That opened a second front in the war, which was disastrous for the Hitler regime.

Oman's government has, so far, ignored Trump's threat.
 

Why does this matter?

• Presidents who can't remember which side is which in a war aren't mentally fit for office. 

• The problem with making so blindingly stupid a threat is that your allies have to take it seriously while your enemies can laugh it off.