Senator Thad Cochran won Democrats' support. Photographer: Justin Sullivan/Getty Images
Senator Thad Cochran won Democrats' support. Photographer: Justin Sullivan/Getty Images

Democrats took part this week in the biggest party raid since Watergate -- and it was far more successful.

Democrats in Mississippi helped save Republican Senator Thad Cochran’s political career by pulling off a legal but controversial tactic that, ironically, they had tried to eliminate not long ago. A party raid is when one party seeks to determine another party’s nominees by voting in its primary (although it meant something rather different to President Richard Nixon). It is rarely attempted in any organized fashion, and it is almost never successful, at least not in major races.

This year's Mississippi primary was different. The Cochran campaign made a concerted effort to drive Democrats to the polls, a move that won the support of many Democratic leaders, including many black leaders. Analysis of voter turnout data suggests that Democratic votes played a crucial role in Cochran’s victory.

It was an interesting turnabout for the state’s Democratic Party in general and black leaders in particular, who together had tried to end party raiding beginning in 2003. After failing to win approval for a closed primary from the state attorney general and the U.S. Department of Justice, the party filed suit in federal court, shortly before the 2006 primaries.

That year, one of the state’s tightest congressional races was between a longtime Democratic incumbent, who was black and liberal, and a primary challenger who was white and moderate. Black leaders supporting the suit hoped that a closed primary would prevent white Republicans from raiding the primary and defeating the incumbent. This year, the roles were reversed: Black leaders encouraged voters to raid a primary to support the incumbent.

In 2006, a federal judge ruled in the Democratic Party’s favor, ordering the state to adopt a system of voter registration by party. The decision was reversed on a technicality; had it held, Democrats wouldn't have been able to vote for Cochran and Chris McDaniel may well have won.

The experience of Mississippi Democrats is a useful reminder that it’s dangerous to support election laws based on partisan calculations. It’s possible that McDaniel’s loss -- and accusations, not supported by the evidence, that Democrats brought down House Majority Leader Eric Cantor -- will result in a push by Tea Party activists to close Republican primaries to Democrats in various states. Before going down that road, Republicans ought to recognize that party raiding is as likely to help their candidates as hurt them.

When party raiding occurs, it can happen in one of two ways: People who are not members of the party can vote for the candidate they find least objectionable, as Democrats did with Cochran. Or they can vote for the candidate they believe will make the weakest general election opponent. The latter strategy only works, however, if the side doing the raiding has a hope of winning the general election.

In Mississippi, voters haven’t elected a Democrat to the Senate since 1982. So the primary was, in effect, Democrats’ only real chance to influence who holds the seat. If, on the other hand, McDaniel and Cochran were running in a state with more evenly matched parties and more competitive general elections, Democrats may have crossed over in support of McDaniel, knowing that it would give their own party’s nominee a better shot in November.

Across the country, party raids can help Tea Party candidates or hurt them, depending on the situation. Trying to end raids by closing the primary, however, would almost certainly hurt the Republican Party as a whole, by amplifying the voices of Tea Party activists.

In 2010, for instance, Tea Party favorite Sharron Angle won Nevada’s closed party primary over several more moderate candidates. If Democrats had been allowed to raid the Republican primary, they probably would have supported her -- and the party was practically gleeful when she won. That year, Democratic senatorial candidates in Colorado and Delaware, which also hold closed primaries, were equally pleased to face Tea Party opponents who defeated more moderate opponents. Democrats won all of those races.

In most cases, Democrats would gladly trade the possibility of a rare party raid for a closed Republican primary. But it’s a trade that Republicans would be foolish to accept.

To contact the writer of this article: Francis Barry at fbarry5@bloomberg.net.

To contact the editor of this article: Christopher Flavelle at cflavelle@bloomberg.net.