In the 1984 election Ronal Regan received 525 (97.58%) of the 538 electoral votes. In the 1936 election Franklin D. Roosevelt received 523 (98.49%) of the 531 electoral votes. In the 1972 election Richard Nixon received 520 (96.65%) of the 538 electoral votes. In the 1820 election James Monroe was unopposed and received 231 (99.57%) of the 232 electoral votes. George Washington received 100% of the electoral votes and was unanimously elected President in 1789 and 1792.
Congress
2/3
Well as the population has grown over time, it is impossible to answer this properly in absolute terms, perhaps it would be better to ask your question again regarding the greatest percentage of the vote.
He presides over the US Senate and votes in the event of tie. He is next in line for the Presidency if the president is incapacitated.
Over 50%
2/3
The same type it was before, the count of votes for an elected official does not change the form of government.
House elects the president if no candidate has over 50% of the electoral college votes.
Any citizen over the age of 18 can vote for who they choose, then the electoral college takes the votes from the citizens and does a final vote.
The procedure for counting electoral votes in the United States is outlined in the U.S. Constitution. The Vice President, as President of the Senate, presides over a joint session of Congress where the votes are counted. The electoral votes from each state are first presented alphabetically, and then the Vice President announces the results and declares the winner.
Popular votes are cast on the Tuesday after Nov. 1 and before Nov. 9. Electoral votes are cast on the Monday after Dec. 12 and before Dec. 20. Electoral votes are counted on Jan. 6. The new Congress begins its elections of the president and/or vice president after that if necessary. The new terms for president and vice president begin at noon EST on Jan. 20.
Just over 9 million (http://www.realclearpolitics.com/epolls/2008/president/republican_vote_count.html