What did Donald Trump do today?

He let Fox News cancel his moon shot.

On March 24 of this year, Trump issued a statement titled "President Donald J. Trump Is Boldly Putting Americans Back on the Moon," in which he directed NASA to move the date of its next planned moon mission from 2028 to 2024. (NASA hadn't been told any such order was coming.)

He tweeted about it just last month:

Today, Trump tweeted that "NASA should NOT be talking about going to the Moon - We did that 50 years ago."

Trump often forgets what his policies are on basic issues, which can make his sudden reversals hard to explain. But in this case, it's pretty clear what prompted this policy change: he was having "executive" time aboard Air Force One, watching TV and tweeting. Just before Trump's tweet, Fox News host Neil Cavuto had complained that NASA was

refocusing on the moon, the next sort of quest, if you will, but didn't we do this moon thing quite a few decades ago?

Who cares?

• Presidents should base their policy decisions on expert knowledge, not offhand comments by TV anchors.

• It's bad if the president doesn't know or care what he believed less than a month ago.

• You can think that the United States should or shouldn't go to the moon, but not both.