But just because a president has the power to declassify (and make classified) anything he wants, it doesn't necessarily mean that it is wise. Showing off your toys is fine when it is a jet with a bathroom covered in gold leaf. When a tweet reveals capabilities that your country spent (literally) billions of dollars on, you are basically wasting taxpayer's money, because now these satellites are going to be less effective. How much less effective probably depends on the adversary, since the big players probably had a good guess about what these imaging satellites could do, but I'll bet ISIS probably didn't (similar to how an unfortunate comment alerted ISIS about being tracked by geotagged images on social media).

It might be okay if experts conversed with the president about the second and third order effects of tweeting the image, and he concluded that it was worth it to release the image. However, given the widely reported disdain that he has for the intelligence community I doubt that such a conversation took place.