The 25 year deadline to declassify them was set in the President John F. Kennedy Assassination Records Collection Act of 1992, signed by George Bush senior
He didn't declassify them. They were scheduled to be declassified. Trump's involvement was that the IC asked him to stop them from being declassified and he ignored their request, probably out of spite for the IC.
What's the chance these documents are not actually true? If I was the CIA I would use these leaks to declassify false information about my enemies, hoping to destabilise their regimes.
I also liked the snide remark in the article about how these presidents were CIA employees who governed Mexico "in their spare time."