Republican Dino Rossi will likely enter the race to challenge Sen. Patty Murray (D-WA). Rossi is a well-known Republican in Washington State and has twice unsuccessfully run for Governor. But the GOP considers him a top recruit. More evidence: The DSCC has been flooding my inbox with anti-Rossi e-mails, indicating that Democrats think he is a legitimate challenger.
Rossi is the not the only Republican in the race. A host of other potential challengers includes Clint Didier (who just received Sarah Palin's endorsement), Don Benton and Paul Akers.
The important thing about Washington is that it does not hold party primaries in the traditional sense. The state recently adopted a top-two primary system. (California voters are likely to approve a ballot measure on June 8 that would enact a similar method.)
In this system, all candidates run on the same ballot in the August primary. The two candidates who get the most votes, regardless of party, are the only ones who appear on the general election ballot in November. In theory, the November election could be between just two Democrats or just two Republicans.
Given this system and the fact that the Republican field is crowded, Democrats should think about strategically running another Democratic candidate in the Senate primary in addition to Murray. With heavy competition among Republicans, it is possible they would split the Republican-leaning vote. Democrats could turn out their base, leaving Murray plus the additional Democrat as the top-two vote getters. If that happens, only the Democrats would appear on the November ballot. It would be a way for Democrats to make sure they hold on to the Senate by August, letting them focus their energy on other races in November.