The End of Term Archive is a collaboration between the Internet Archive and a number of libraries. It archives government websites at the end of presidential administrations and makes them available on its website as well as within the Wayback Machine. Archives are available going back through the 2008 presidential transition.
Using the Archive
If you know the exact URL of the government website you're interested in accessing, enter it in the Wayback Machine, then select the date and time of the version you want. Alternatively, you can try the beta version to search by keyword.
The End of Term Archive page provides more advanced options for finding the pages you want. The menu on the left allows you to browse based on transition year (2008-2009, 2012-2013, or all). Once you've reached the browse page, you can sort by title or filter by year and government agency domain (House, Senate, Supreme Court, etc.). You can also do keyword and full text searches from the End of Term Archive page, which may provide slightly more focus and detail than similar searches conducted directly in the Wayback Machine.
Nomination and Archiving Process
As the project ramps up during the months leading up to transition periods, participants identify a broad range of sites to be archived while also working with government information and subject area specialists to identify the highest priority websites for special attention. Additionally, anyone can nominate URLs for inclusion using an online nomination tool.
The End of Term 2016-2017 archive project is currently underway, and you can nominate sites for inclusion using the tool below until March 1, 2017. You can also get a sense of what will likely be included by looking at past archives and at what sites have been nominated for inclusion.
The National Archives and Records Administration (NARA) curates and provides access to the National Archives, the U.S. Government's public collection of archived government and historical records. Their website contains a wealth of electronically available government information, but is not specifically focused on web-based materials.
Official Archived Web Pages
At the end of each presidential administration, NARA creates official archived versions of important web pages and other online materials such as social media accounts. For example, you can view the official archive of the Obama White House website at http://obamawhitehouse.archives.gov. Barack Obama's presidential Twitter account is also still accessible using the handle @POTUS44.
The Library of Congress maintains thematic web and event-based archives related to topics in U.S. history, law, and government. The available sites and pages may also be archived in the Wayback Machine as well. The Library of Congress interface allows advanced filtering options by location, subject, language, and more, or you can browse through themed collections. This is a great place to start if you are looking for archived web resources surrounding a specific topic, but don't know the exact URLs that interest you.
Perma.cc is a service developed and maintained by the Harvard Law School Library that helps legal scholars and courts create links to web citations that will never break or disappear. When a user creates a Perma.cc link, Perma.cc creates a permanent link to an archived record of the page and its content. Even if the original source is no longer available, the archived page will continue to be accessible through the Perma.cc link. This is a very helpful tool to prevent link rot and preserve the integrity of legal citations on the web, but it is not necessarily useful for doing research. Content saved in Perma can only be found using the direct link, so unless you have the precise Perma.cc link you will not be able to find the archived URL.
In December 2018 the Presererving Electronic Government Information (PEGI) project released a report describing efforts to preserve government information and data within the United States. This report may be useful to researchers who wish to understand the scope of efforts that exist to preserve government content.