What did Donald Trump do today?

He found a reason to get genuinely upset with Iran.

Last Friday, Trump scrambled to come up with a heroic explanation for why he'd launched and then canceled a retaliatory strike against Iran. While Trump's story changed several times over the course of the news cycle, the core of it was that Trump felt that killing perhaps 150 Iranians was out of proportion for shooting down an unmanned piece of military hardware. It was a rare dovish moment for Trump, who went so far as to suggest that the whole thing had been a simple "mistake" on the part of low-level Iranian officers.

Four days later, Trump's new official position is that if Iran hurts "anything American," human or machine, it will result in "overwhelming force" leading to "obliteration."

The reason for this radical shift appears to be that Iranian President Hassan Rouhani insulted him. Rouhani said that Trump's impositions of new sanctions was "idiotic and outrageous." Rouhani also said that Trump was showing signs of mental illness.

Trump's tweet-rant complaining about the "ignorant and insulting" statement and threatening "obliteration" appeared almost immediately after Rouhani's remarks appeared in the news.

Why does this matter?

• It's dangerous for America's national security if the president can be this easily baited.

• Military decisions should be made based on what is best for the country, not how well the president can control his temper.