On Election Day, Louisiana Sen. Mary Landrieu, a Democrat, faced off in a primary against eight other candidates, including three major Republican challengers. Because she didn't win 50 percent of the vote, she now must compete in a runoff—though all other states have already picked their senators. How did Louisiana get such an odd election system?
Every state, local, and congressional election in Louisiana is decided by what's called an open primary. The rules are that all candidates for a single office, regardless of party, appear on the same ballot on Election Day, and all voters (again regardless of party) can vote for any one of them. If no candidate wins 50 percent of the vote, a runoff between the top two vote-getters takes place a month later. It's completely possible for the open primary to produce a runoff between two Democrats or between two Republicans.
Ironically, the system that helped the GOP make re-election difficult for Landrieu was put in place in 1975 by a Democrat, then Gov. (and now convicted felon) Edwin Edwards. In the 1970s, the South was still largely a Democratic stronghold, and incumbents like Edwards often faced their stiffest challenges in Democratic primaries. So Edwards pushed to do away withthe traditional party-primary system. The strategy paid off. In 1975, facing weak opposition, he cruised to re-election.
The open primary has been criticized for forcing voters go to the polls twice in the space of a month, which tends to depress turnout. Some academics contend that it favors incumbents (who can afford to campaign twice) while others say it aids fringe candidates (who can get just enough votes to force a runoff). In 1991, former Ku Klux Klan member David Duke used the open primary system to force a runoff with Edwards. Thus originated the famous bumper sticker: "Vote for the Crook: It's Important."
Louisiana's election system used to be even stranger. Until 1997, the open primary was held in October, which meant that if a candidate got over 50 percent he could be elected to Congress a month before the federal Election Day. The Supreme Court told Louisiana to knock it off. So the state pushed its open primary back a month, and now instead of electing candidates early, it frequently elects them late.
Explainer thanks M. David Gelfand of Tulane University Law School; Rashad Robinson of the Center for Voting and Democracy; and Catherine Lemann of the Law Library of Louisiana.