Michigan's 7th Congressional District, which stretches from Lenawee and Hillsdale counties west to include Battle Creek, Jackson, and some Ann Arbor and Lansing suburbs, has gone from being one of the nation's most predictable Republican districts to one of the nation's most volatile. It has sent a different man to Washington in each of the past four elections.
After longtime incumbent Nick Smith retired in 2004, voters rejected his son in favor of Joe Schwarz, a moderate-to-liberal Republican state senator. Mr. Schwarz was defeated two years later in the GOP primary by Tim Walberg, an ultra-conservative former Bible salesman. Mr. Walberg was narrowly elected in 2006 - and then narrowly defeated in the Obama landslide of 2008 by Democrat Mark Schauer.
This district is one of the GOP's top targets this year. A fierce and expensive battle for tomorrow's primary election has been waged between Mr. Walberg, 59, who wants his old seat back, and Brian Rooney, 37, a constitutional lawyer and Iraq war veteran who is a member of the family that owns the Pittsburgh Steelers football team.
A third GOP candidate, local businessman Marvin Carlson, is trailing far behind. There is little to separate the candidates on the issues, but some analysts think Mr. Rooney may have a better background and a better chance to retake the seat for the Republicans.
Although the district leans Republican, Mr. Walberg's views are to the right of even some in his own party. Among them are the man he defeated, former congressman Schwarz, who endorsed Mr. Walberg's Democratic rival last time.
The winner of Tuesday's primary will be in for a fight. Mr. Schauer may be a freshman and an underdog, but he has worked hard on issues of concern to voters and has a solid base of support in the district's cities.
Expect this to be one of this year's most closely fought - and expensive - congressional elections.