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The coattail effect or down-ballot effect is the tendency for a popular political party leader to attract votes for other candidates of the same party in an election. For example, in the United States, the party of a victorious presidential candidate will often win many seats in Congress as well; these Members of Congress are voted into office "on the coattails" of the president.
This theory is prevalent at all levels of government. A popular statewide candidate for governor or senator can attract support for down ballot races of their party as well.
This also refers to the phenomenon that members of the U.S. Senate or House of Representatives are more likely to be voted for on a year of the presidential election than a midterm.
The "coattail effect" is not usually caused by a popular candidate convincing swing voters to cast their ballots for their party, although this is not unheard of. Rather, the effect often stems from popular candidates driving voter turnout among their own party base, people who are likely to vote for downballot party candidates anyway.
The "coattail effect" has also been used to derogatorily describe the effect of Group Representation Constituencies (GRCs) in Singapore, where candidates for Parliament run on a party slate of 3 to 6 candidates. This allows weak candidates to get elected "riding on the coattails" of strong candidates on their slate.
Riding the coattails is a metaphor that refers to one who achieves some level of success or notability primarily through association with someone else. This can often be used as a generic phrase for anyone that hangs onto another person as they forge ahead, without effort from the hanger-on.
Presidential coattails is the ability of a Presidential candidate to bring out supporters who then vote for his party's candidates for other offices. In effect, the other candidates are said to ride on his coattails. Before the introduction of the secret ballot in the late 19th century, voters cast their ballots by taking a ticket provided by a party worker and putting it in the ballot box. The party-column ballot listed all candidates of the party in a single column and allowed the voter to mark off the party box at the top, which encouraged straight-party voting and the coattails effect. Straight-party voting was the norm, and winners in Presidential elections often had long coattails. They almost always began their term with majorities in the House and Senate.
In modern times voting machines have replaced the party-column ballot with the office-column ballot: candidates are grouped by office rather than party. Often there is no way to cast a party-line vote, and each office must be voted on separately. The proportion of voters choosing House and Presidential candidates of different parties increased from 13 percent in 1952 to more than 40 percent in the elections of 1972, 1980, and 1988. Consequently, Presidential coattails have been virtually eliminated in most elections, and a number of Presidents--including Richard Nixon, Ronald Reagan, and George H. W. Bush--have begun their terms with one or both chambers of Congress controlled by the opposition party.
Presidents may suffer from a "reverse coattail" effect, in which their party's candidates for the House or Senate get more votes than the president's themselves. In 1976, for example, Jimmy Carter won the White House with 40,420,420 votes, but Democratic candidates for the House that year received 41,749,411 votes. In 1992 almost all Democrats elected to Congress won more votes in their congressional districts than the party's Presidential candidate, Bill Clinton; this may have had to do with the presence of a strong third-party presidential candidate, Ross Perot.
There is also the "negative coattail" effect, in which a controversial Presidential candidate may hurt candidates on the party's ticket running for lower offices. Barry Goldwater's poor showing in the Presidential election of 1964 led to the defeat of dozens of Republicans in the House of Representatives, leaving President Lyndon Johnson a large Democratic majority to pass his agenda. The negative coattail effect is also common in midterm elections - when a President associated with unpopular policies is not up for re-election, the electorate will often respond by punishing Congressional candidates from the President's own party. The Presidential elections of 1948 and 1952 are the most recent elections in which the same party both won the White House and took control of the House from their opponents. Since 1952, control of the House has changed hands four times, all of which were in midterm elections (1954, 1994, 2006 and 2010) and all of which were at the expense of the incumbent President's party.
Since the end of World War II, there have been a total of five American presidential elections which had coattail effects: Harry Truman in 1948, Dwight Eisenhower in 1952, Lyndon Johnson in 1964, Ronald Reagan in 1980, and Barack Obama in 2008.
Singapore introduced the GRC system in 1969, where candidates for Parliament run and are elected on a slate of 3 to 6 candidates in some constituencies, with a minimum of one minority candidate on each slate. The purported aim was to ensure minority representation in Parliament. However, it resulted in a "coattail effect" where unpopular and even unknown candidates are elected because they ran together with popular candidates (usually Ministers) on the same slate.
Despite the official reason cited, it was later stated by former Prime Minister Goh Chok Tong that it was used to recruit able people to join politics, particularly since the GRC system reduced the losses of the ruling party. In Singapore, the ruling People's Action Party maintains almost total dominance in Parliament with the GRC system. As of 2009, there were only 6 fully elected Opposition MPs in the 69-seat Parliament.