An American voter often has to choose between a Democrat candidate and a Republican candidate, neither of whom the voter likes. A vote is cast for “the lesser of two evils”—the least worst candidate.
 
In 1980, the two political parties presented the presidential choice between Jimmy Carter (Democrat) and Ronald Reagan (Republican). Many pundits—and even a bumper sticker—called it a choice of “the evil of two lessers.” The term “evil of two lessers” had been previously used in graffiti during the 1968 presidential election between Hubert Humphrey (Democrat) and Richard Nixon (Republican).
 
American journalist and author Max Lerner (1902-1992) wrote in 1949, “When you choose the lesser of two evils, always remember that it is still an evil.”
     
 
Wikipedia: Lesser of two evils principle
The lesser of two evils principle, also known simply as the lesser evil, is the idea that of two bad choices, one isn’t as bad as the other, and should be chosen over the one that is a greater threat.
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Modern usage in American politics
The lesser of two evils principle is today most commonly used in reference to electoral politics, particularly in Western nations, and perhaps in the United States more than anywhere else. When popular opinion in the United States is confronted with what is often seen as two main candidates — normally Democrat and Republican in the modern era — that are substantially similar ideologically, politically, and/or in their economic programmes, a voter is often advised to choose the “lesser of two evils” to avoid having the supposedly “greater evil” get into office and wreak havoc on society. Opponents of this line of thinking include revolutionaries who oppose the system as a whole, and political moderates advocating that third parties be given greater exposure in that system.
 
For a particular voter in an election with more than two candidates, if the voter believes the most preferred candidate cannot win, the voter may be tempted to vote for the most favored viable candidate as the lesser of two evils.
 
Supporters of lesser-evil tactics often cite United States politician Ralph Nader’s presidential campaign as an example of what can happen when the third-party candidate is still voted for. In 2000 as the United States Green Party candidate, he garnered 2.7% of the popular vote and, as a result, is considered by many U.S. Democrats to have tipped the election to George W. Bush. One counterargument is that Nader’s candidacy likely increased turnout among liberals and that Al Gore took four of the five states - and thirty of the fifty-five electoral college votes - in which the outcome was decided by less than one percent of the vote.
   
Google Books
Encyclopedia of Graffiti
By Robert George Reisner and Lorraine Wechsler
New York, NY: Macmillan
1974
Pg. 252:
Richard Nixon the evil of two lessers.
(On a billboard in subway during the 1968 Humphrey-Nixon campaign)
 
29 July 1975, Pocono Record (Stroudsburg, PA), “Let’s look at Ford as we once scrutinized Presidents” by James Perry, pg. 4, col. 4:
Reagan, a wit has suggested, is the evil of two lessers. In fact, there’s not much difference between Ford and Reagan.
   
Google News Archive
9 June 1980, Eugene (OR) Register-Guard, “Quotable,” pg. 16A, col. 2:
Herb Caen in the San Francisco Chronicle:
“We don’t always vote for the lesser of two evils. Just seems that way, especially this year. In 1972, we voted for the evil of two lessers, remember?”
 
23 June 1980, Chicago (IL) Tribune, “How campaigns could test for ability, not packaging” by Alex Seith, sec. 4, pg. C2:
With acid humor, a disgruntled pundit calls the choice between Jimmy Carter and Ronald Reagan “the evil of two lessers.”
     
Google News Archive
28 September 1980, New York (NY) Times, pg. E21:
WASHINGTON
The Evil Of 2 Lessers
By James Reston
WASHINGTON, Sept. 27—One of the funny things about this Presidential election is that Carter and Reagan seem determined to give the impression that they are actually worse than they really are.
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Most of the cliches of the campaign are either inaccurate or misleading, including the popular complaint that the people are being forced to choose between “the lesser of two evils.” The most important fact is that they are probably going to have to endure, for four long years, the evils of two lessers, who won’t have much confidence at home or abroad. It’s a puzzle why each of the two leading candidates insists on putting his worst foot forward.
 
Google Books
A Tide of Discontent:
The 1980 elections and their meaning
By Ellis Sandoz and Cecil Van Meter Crabb
Washington, DC: Congressional Quarterly Press
1981
Pg. ?:
One entrepreneur manufactured bumper stickers celebrating the presidential election as a choice between “the evil of two lessers.”
   
Google Books
The Election of 1980:
Reports and interpretations
By Gerald M. Pomper
1981
Pg. 74:
Instead, it was to be a forced choice of the “lesser of two (or more) evils,” leading one wag to bewail “the evil of two lessers.”