Hi There, This is a bit more of a meta-history question, but i've often come across stories built around some preserved document from government history in the US, the most obvious example is William Safire's Moon disaster speech.
Who holds on to these? I feel like it might be the library of congress, but i remember it being mentioned in The West Wing (sources, amiright?) that is was the treasury. I can't find anything on this, so I'm curious if one of you folks knew.
Follow up: when did they realize that all this stuff was worth keeping?
The National Archives and Records Administration maintains the official records of the United States government.
The Library of Congress is responsible for collecting non-governmental materials, including books, music, film, television, and non-governmental archives.
The National Archives and Records Administration (NARA) is responsible for the retention and disposition of official records of the US federal government. It has, at this point, very complex and baroque regulations governing record retention and what kinds of things they have to give to NARA. According to them about 1-3% of all US records are retained indefinitely (which is a massive amount, when you consider how much information is created by the federal government). It is not a haphazard process — if anything it may be over-bureaucratized.
NARA was created by Congress in 1934 as a central institution for this record management. Prior to that, records were maintained but in a more haphazard form by different agencies. Many agencies still maintain their own archival record systems, of course, though in theory after some amount of time they are meant to be transferred to NARA custody. (As you can imagine, compliance is often limited by time and budget — for no agency other than NARA is historical record retention their primary function, and true to American approaches to government, NARA is perpetually underfunded for the amount of work that is given to it.) NARA has many facilities across the country, some of which are for researchers, some of which are just basically warehouses.
I am not sure to what degree Congress itself is bound by these laws — they often make themselves an exemption (like they did with Freedom of Information Act). There is a Congressional Records section of NARA which contains the records of many Congressional committees, but I don't know whether their regulations are as ironclad as it is with federal agencies. (The Archivists I have talked to at NARA make it sound like stuff just sort of shows up from Congress whenever it shows up, like Congress works on its own system internally. But it may just look that way from where they are sitting.)
There are other places where governmental records can end up, like Library of Congress, but NARA is meant to be the main repository of archival information. LOC's holdings are mostly of published material and some personal archival collections (as opposed to official agency collections).
The Library of Congress and the National Records Administration hold official records. Presidential libraries and other small repositories exist as well, such as archives for military units.