e to organize under such electoral systems than they do in the United States.—Schmidt, Shelley, Bardes (2008), 
In contrast, a voting system that allows only a single winner for each possible legislative seat is sometimes termed a plurality voting system or single-winner voting system and is usually described under the heading of a winner–takes–all arrangement. Each voter can cast a single vote for any candidate within any given legislative district, but the candidate with the most votes wins the seat, although variants, such as requiring a majority, are sometimes used. What happens is that in a general election, a party that consistently comes in third in every district is unlikely to win any legislative seats even if there is a significant proportion of the electorate favoring its positions. This arrangement strongly favors large and well–organized political parties that are able to appeal to voters in many districts and hence win many seats, and discourages smaller or regional parties. Politically oriented people consider their only realistic way to capture political power is to be either a Republican or Democrat.
In the U.S., forty-eight states have a standard winner-takes-all electoral system for amassing presidential votes in the Electoral College system. The winner–takes–all principle applies in presidential elections, since if a presidential candidate gets the most votes in any particular state, all of the electoral votes from that state are awarded. In all but two states, Maine and Nebraska, the presidential candidate winning a plurality of votes wins all of the electoral votes, a practice called the unit rule.
Duverger concluded that "plurality election single-ballot procedures are likely to produce two-party systems, whereas proportional representation and runoff designs encourage multipartyism." He suggested there were two reasons why winner–takes–all systems leads to a two-party system. First, the weaker parties are pressured to form an alliance, sometimes called a fusion, to try to become big enough to challenge a large dominant party and, in so doing, gain political clout in the legislature. Second, voters learn, over time, not to vote for candidates outside of one of the two large parties since their votes for third party candidates are usually ineffectual. As a result, weaker parties are eliminated by voters over time. Duverger pointed to statistics and tactics to suggest that voters tended to gravitate towards one of the two main parties, a phenomenon which he called polarization, and tend to shun third parties. For example, some analysts suggest that the Electoral College system in the United States, by favoring a system of winner–takes–all in presidential elections, is a structural choice favoring only two major parties.
Gary Cox suggested that America's two-party system was highly related with economic prosperity in the country:
The bounty of the American economy, the fluidity of American society, the remarkable unity of the American people, and, most important, the success of the American experiment have all mitigated against the emergence of large dissenting groups that would seek satisfaction of their special needs through the formation of political parties.—Cox, according to George Edwards
An effort in 2012 by centrist groups to promote ballot access by Third Party candidates called Americans Elect spent $15 million to get ballot access but failed to elect any candidates. The lack of choice in a two-party model in politics has often been compared to the variety of choices in the marketplace.
Politics has lagged our social and business evolution ... There are 30 brands of Pringles in our local grocery store. How is it that Americans have so much selection for potato chips and only two brands — and not very good ones — for political parties?—Scott Ehredt of the Centrist Alliance
Third parties, meaning a party other than one of the two dominant parties, are possible in two-party systems, but they are often unlikely to exert much influence by gaining control of legislatures or by winning elections. W