You can find the results of past federal elections from several government sources.
Federal Election Commission Resources
Every two years, the Federal Election Commission (FEC) releases the official results from each state’s federal elections. The information covers elections from 1982 to 2014 and includes primary, runoff, and general election results for:
- U.S. Senate
- U.S. House of Representatives
- U.S. President (for years when there is a Presidential election)
National Archives Resources
You can find the details of the 2000, 2004, 2008, and 2012 Presidential elections and counts for electoral college votes versus popular votes on the National Archives and Records Administration's Historical Election Results page. And you can see the "box scores" for all elections from 1789 to 2012.
House of Representatives Resources
Find the statistics from every federal election from 1920 through 2012 from the Office of the Clerk of the U.S. House of Representatives. The results, in PDF format, are organized by state and include Washington D.C. and the U.S. territories. They show the official vote counts for every candidate for President, Senator, and U.S. Representative.