1 Answers
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. Popular statewide candidates for governor or senator can attract support for down ballot races of their party as well.
This is prevalent in the United Kingdom and Canada especially in a general election. People have a tendency to vote on the basis of a political party instead of the MP for their area.
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.