thanks to the Freedom of Information Act that was passed by Democrats over the objections of Cheney, Rumsfeld and Scalia.
What you are referring to are the amendments to the FOIA in 1974. The FOIA itself was passed in 1966 and signed into law by President Lyndon Johnson.
President Ford vetoed the amendments to FOIA, but was overridden by congress. The House voted 371-31 to override the veto, and the Senate voted 65-27.
If you want to read the full story, I suggest looking here, as there are links to scans of the actual documents involved.
Weirdly enough, Johnson was against FOIA, and Rumsfeld was originally for it.