The United States has had 55 Presidential elections. The first nine have very poor records existing of the popular vote and I will not consider those.  Of the remaining 46, fourteen of the winners received less than half of the popular vote.  There were more than two candidates in all of these fourteen.

          In 1824, Andrew jackson had 43% of the popular vote to John Quincy Adam's 30.5%, but Henry Clay threw his 13% to Adams to allow him to win the electoral college vote. The 1844 election was won by James Polk with a popular vote of just under 50%.  In New York, the anti-slavery Liberty Party's Birney received 15,800 votes, more than Polk's margin of 5,100 votes.  A victory in New York would have given Henry Clay a 141-134 edge in the electoral college.  In 1848 Zachary Taylor won with only 48% of the popular vote when the Democrat vote was split between their candidate Cass and the splintered Free soil party.  Abraham Lincoln was elected with only 41% of the popular vote in 1860 when three other candidates split the remaining votes.  Close numbers also mark the elections of 1880, 1884, 1892, and 1948 (Truman over Dewey).  Theodore Roosevelt split the Republican vote (a nine per cent advantage) in 1912 to allow Woodrow Wilson a electoral coup.  Nixon's close victory in 1968  might have been a landslide without George Wallace and his 13%.  In 1992, Clinton won with  only 43% of the popular vote when third party candidate Ross Perot"s 19% certainly reduced Bush the elder's almost 38%. 

    The remaining three are interesting in that winning the popular vote did not assure the presidency.  The Compromise of 1877 marred the 1876 election when three states' electoral votes were disputed and Rutherford Hayes became President although Samuel Tilden had received over 51% of the popular vote.  In 1888 Benjamin Harrison had more popular votes but Grover Cleveland got more electoral votes as George Bush did in 2000, although Gore received about 400,000  more votes and would easily have won if Nadar had dropped out.  (Florida would not have been so close if the news media had not announced the polls were closed in Florida when in the conservative pan handle, a different time zone, the polls were still open for another hour.)  

    The electoral College is the law of the land, and I am not saying it is wrong or should be changed: that is a different question. The only point I am attempting to make is that a third candidate often drastically effects the results. How different our country might be today if Teddy Roosevelt had not run in 1912.  Perhaps if Huckabee had dropped out of the Republican race a month ago, Romney might be the front runner.  Perhaps not.  But we can never know how our history has been effected by third running candidates in not only the Presidential elections, but also the primaries, and lesser elections.