The 2018 midterm elections are about to heat up. Much of the focus is on which of the two major parties will have control of Congress after November 6 -- are we looking at a blue wave or a red wave?

What gets less attention are the third party and independent candidates who are trying to break through the two-party duopoly and offer voters an alternative. Candidates like Gary Johnson, who arguably stands the best chance of being the first member of the Libertarian Party to be elected to the upper chamber of Congress.

Independent and third party candidates, like Johnson, face uphill challenges throughout the entire election process to just be competitive. Competition in elections is so bad that most Americans think it's impossible for candidates outside the two parties to win.

It is important to note that, though the political landscape and system have changed to various degrees throughout history, there have been several independent and third party senators in U.S. history. Probably more than you think!

In total there have been 77 independent or third party U.S. senators from Senator Robert Hayne in 1831, all the way up to Senator Angus King (ME) from 2013 until the present.

Robert Hayne was a member of the Nullifier Party, an early American party founded in South Carolina by John C. Calhoun, another third party senator and a Nullifier, as well as the seventh Vice President of the United States (first under President John Quincy Adams, then under President Andrew Jackson).

The Nullifier Party was a states' rights party committed to the Virginia and Kentucky Resolutions, which hold that states can nullify unconstitutional federal laws within their borders (a kind of judicial review of congressional legislation). A recent example of soft nullification would be California legalizing marijuana in opposition to federal law, and 29 other states and the District of Columbia following suit.

The Nullifier Party was nearly the nation's first third party, but was narrowly beat for that distinction by the Anti-Masonic Party, which was created in New York in February 1828.

Another more recent independent or third party senator is Bernie Sanders (VT), an independent who caucuses with the Democratic Party in the Senate chamber.

Three of these 77 senators in U.S. history had also been a major party candidate at one time, like Joe Lieberman (I-CT), who was defeated in a Democratic Primary in his state, and ran as an independent to win the general election.

James Buckley was a Conservative Party senator from New York from 1971 to 1977. Ernest Lundeen was a Farmer-Labor Party senator from Minnesota from 1937 to 1940, and there were three other Farmer-Labor Party senators in the 1920s and 1930s.

The Farmer Labor Party was formed in Minnesota in 1918, to look out for farmers and laborers, who saw their purchasing power vastly diminished by war time inflation.

In the late 1800s, there were several Silver and Silver Republican Party senators. These third parties, popular mostly in Western states with high silver output, split off from the Republican Party in support of "bimetallism," which meant inflating the gold-backed dollar currency with silver. Midwestern farmers faced with a heavy credit burden also supported this idea to make it easier to pay off debts.

Though successful independent and third party bids for major national offices have come to be viewed as quixotic and unlikely, U.S. history abounds with examples of such candidacies winning popular support with voters at the ballot booth.