In primary elections in the United States, crossover voting refers to a behavior in which voters cast ballots for a party with which they are not traditionally affiliated.
[1][2] Even in the instance of closed primary elections, in which voters are required to receive a ballot matching their political party, crossover voting may still take place, but requires the additional step of voters to change their political affiliation ahead of the primary election.
[5] A notable example of attempted party raiding was Operation Chaos in the Democratic primary in 2008, when Rush Limbaugh encouraged Republicans to vote for Hillary Clinton in an effort to weaken Barack Obama politically.
[6] Another occurred in the 2012 Republican primaries, where many Democratic voters in Michigan voted for weaker GOP candidate Rick Santorum over front-runner Mitt Romney in order to disrupt his campaign.
These crossover voters are referred to as "True Supporters",[3] and are not casting their votes for purposes of insurance or sabotage.