What Trump Did Today will return on Saturday, September 12th.

What did Donald Trump do today?

He celebrated the good health of North Korean dictator Kim Jong-un.

This morning, without explanation or any apparent reason for doing so, Trump declared on Twitter that North Korean dictator Kim Jong-un was in good health and warned Americans not to "underestimate" him.

Intense speculation about the physical and political health of the North Korean leader is as old as the country itself. Rumors that Kim was in a coma earlier this summer proved to be false, but the increased public profile of his sister, Kim Yo-jong, raised eyebrows a few weeks ago. But there was nothing in the news that could have prompted this tweet, not even on the eight hours of Fox News that Trump watched last night and this morning, by his own admission.

It's possible that Trump was, at least in his own mind, trying to get out ahead of another embarrassing revelation in Bob Woodward's latest book about him. Trump gave 18 interviews for the book, sometimes calling Woodward late at night to talk, and allowed the reporter to review previously unreleased letters that Kim sent. Trump has often publicly expressed delight at the "beautiful letters" from Kim, and spoken of how they were the reason that he and Kim "fell in love."

Woodward's transcriptions of the letters show them to be transparently flattering to Trump, almost embarrassingly so. Kim refers to Trump as "Excellency," a detail that thrilled Trump, and played on Trump's hatred for President Obama. It's been known for some time how effective they were, given the almost entirely one-sided concessions Trump has made on major diplomatic and military issues to Kim. Woodward reports that CIA analysts called them "masterpieces" of manipulation, adding, "The analysts marveled at the skill someone brought to finding the exact mixture of flattery while appealing to Trump's sense of grandiosity and being center stage in history."

If Woodward's book is the reason Kim's health was on Trump's mind, it's not clear why he thought Americans would find the good health of a hostile nuclear-armed dictator reassuring.

Why does this matter?

• It shouldn't be this easy to manipulate a president.

• There's a difference between diplomacy and open admiration for dictators.