Alaska's Lisa Murkowski: No. 7 on list of ousted incumbents?

Sen. Lisa Murkowski (R) of Alaska could become the seventh congressional incumbent to lose a primary in 2010 if her too-close-to-call race with 'tea party' favorite Joe Miller stays in Mr. Miller's favor. The last time this many incumbents lost primaries was in 2002, when eight representatives and one senator lost before the general election. Here are the ousted incumbents, in the order they lost their primaries.

- Scott Bland, Contributor

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Sen. Arlen Specter (D) of Pennsylvania speaks at the Democratic State Committee meeting in June. His switch from Republican to Democrat didn't help him, in the end. (Gene J. Puskar/AP)

3. Sen. Arlen Specter (D) of Pennsylvania

Almost as soon as Senator Specter switched parties in April 2009, becoming a Democrat after almost 29 years as a Republican senator, the knives were out back home. Rep. Joe Sestak (D), a former admiral, was already thinking about running against Specter in the general election, and despite opposition from national Democrats he decided in August to oppose Specter in the party primary.

Specter quickly became a reliable Democratic vote as he tried to shore up his credentials with progressive primary voters, lending support to health-care reform, financial reform, and Sonia Sotomayor’s nomination to the US Supreme Court. But that wasn’t enough to stave off Mr. Sestak, who cast Specter’s party switch as political opportunism and ran away with the May 18 primary, 54 percent to 46 percent.