The coattail 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 congressmen 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. The term of voting a straight ticket can also be used.