Since World War II, three third party or independent presidential candidates have drawn at least 5% of the popular vote.
The first three occurred at intervals of 12 years.
In 1968, George Wallace, the past and future governor of Alabama at the time, drew 9,906,473 votes (13.5% of the total vote) and carried five states (46 electoral votes) on his American Independent Party line.
In 1980, Rep. John Anderson of Illinois, who earlier in the year had competed for the Republican presidential nomination, garnered 5,720,060 votes (6.6%, 0 electoral votes) that fall as an independent.
In 1992, wealthy Texas businessman Ross Perot polled 19,741,657 votes (18.9%, 0 electoral votes) running as an independent. Perot ran again for president in 1996, taking 8.4% on the Reform Party line.
http://library.cqpress.com/elections/document.php?id=rcookltr-1527-89627-2588519#.UsliYz90nss