My source is Wikipedia. According to Wikipedia, Ed Clark got a whopping 1.06% of the popular vote in 1980, whereas Gary Johnson got a mere 0.99% in 2012.
Agreed, Johnson in 2016 is definitely the Libertarians' best result. One wonders how that could be, with such exceptional candidates on the major party tickets...
The Union Party was not a real Party, it was just what the Republicans rebranded themselves as in 1864 running against the Democrats, who ran George B. McClellan against Republican Lincoln.
The only opposition party of any importance at the time, the Federalists, failed to even have a presidential candidate, only fielding a vice-presidential candidate. They still managed to gain one state, Massachusetts, but its electors cast their votes for Monroe nevertheless.
In fact the decade following the end of the war of 1812 in 1815 is sometimes dubbed the era of single party politics. In 1816 Monroe had already won with 68% of the vote, and in 1824 there were 4 candidates, but all from the same party.
You need to include the "Liberal Republican Party", which achieved 44% of the popular vote in 1872 for Horace Greeley (The Democratic Party did not field its own candidate that year).
Interesting how much third party popularity has declined over time. America is a capitalist society but has become limited to two options for their leaders. You would think their would be more promotion of additional parties to add competition to politics and by the laws of a free market create a better result for the consumers, the citizens.
The problem is that both of the major parties (and the vast majority of media as well) have spent a very long time pushing the idea that your vote only counts if it's for one of the two major parties. Most people won't vote for third parties because they've been conditioned to believe they're "throwing away their vote" if they do that.
It's not clear to me that more parties would help. In parliamentary systems, there are many parties, but ruling coalitions generally only represent a little more than half the voters. What could fix the problem is a system where minority parties were given congressional committees and executive departments in proportion to the votes they receive.
Oddly enough, guessing Union gave me Union, National Union, and Constitutional Union, but not Union Labor. Not that I'm complaining as I wouldn't have guessed the other two that I got had it not been for the add-on. Just found it odd.
Ross Perot should be on here twice because his 1992 Presidential campaign drew 18.9 percent of the vote as an Independent. That's higher than George Wallace's 14 percent as an American Independent.
Might want to update