The domain suffix of a website (the postscript at the end of a web address) can be a good indicator of the the website's authority and accuracy.
National Archives: America's Founding Documents - Declaration of Independence, U.S. Constitution, and Bill of Rights
Primary Documents of American History - Documents related to American history and the formation of the U.S. government
The United States Code - a consolidation and codification by subject matter of U.S. laws
Political Information - search engine for politics, policy, and political news
Federal Election Commission - the Federal Election Commission (FEC) to administer and enforce the Federal Election Campaign Act (FECA)
Google Newspaper Archive - collection of digitized historic and contemporary newspapers from the U.S. and Canada