Once every decade, certain unfortunate incumbents are sucked into a ritual of panic. Census data is released and district lines are redrawn according to their reported populations -- leaving congressmen who have grown accustomed to loyal constituencies in their wake. The Cook Political Report's redistricting guru David Wasserman takes a look at the 10 most nervous Republicans in this click through gallery.
Dan Lungren, CA-03
The incumbent protection plan California passed in 2002 gave this suburban Sacramento district parts of GOP-leaning outlying counties. Now, census results show Sacramento County is large enough to fully contain two districts, which could force Lungren, a nine-term veteran Republican, into a more compact and more Democratic district. In 2010, while many of his GOP colleagues were cruising to reelection, Lungren barely stumbled across the finish line and could be in more serious trouble against the same opponent in 2012.
Ken Calvert, CA-44
A big surge in Latino voter participation in California’s Riverside County explained why Calvert was almost caught napping in 2008: That year, Calvert barely hung on with 51 percent in a race on no one's radar screen. This district is now 45 percent Hispanic, and the 10-term Republican could easily find his Corona home in a 55 percent Hispanic district if redistricting commissioners decide one should be drawn. Of course, Calvert could move to a more Republican neighboring district, but he would face a competitive primary.
Allen West, FL-22
Florida's 22nd CD may be the ugliest gerrymandered patchwork of precincts in the country, and West won one of the ugliest races in the country in 2010, unseating Democrat Ron Klein with a big lift from senior voters in Palm Beach and Broward counties. If new voter-approved anti-gerrymandering measures are enforced (and that's a big if), West's district will have no place to go but into neighboring Democratic precincts, helping to pave the way for Democratic former West Palm Beach Mayor Lois Frankel.
Joe Walsh, IL-08
Illinois Democrats are still stunned by Walsh's shocking defeat of three-term Rep. Melissa Bean last year. After all, Walsh was supposedly a marginalized tea party candidate with so much baggage (he lived outside the district in a home under foreclosure) that local Republicans wouldn't even carry his literature. So Democrats will do everything they can to make Walsh a one-term wonder. They could make the 8th CD even more Democratic by adding heavily Hispanic Elgin, or they could combine it with veteran GOP Rep. Don Manzullo's 16th CD.
Bob Dold, IL-10
After winning GOP Sen. Mark Kirk's open House seat impressively last fall, Dold now has the most Democratic district of any Republican in the country. As such, it's going to be hard for Democrats to make this district even bluer, but they could try by adding Skokie or other parts of the North Shore. Even if they don't alter the 10th CD's partisan fundamentals, Democrats could weaken Dold simply by giving him hundreds of thousands of new and unfamiliar voters.
Judy Biggert, IL-13
Illinois Democrats probably won't be content to wait until Biggert retires to make a play for her suburban seat. At 73, Biggert is one of the few socially liberal Republicans remaining in the House and has proven a strong general-election candidate, winning seven elections in a row. So Democrats could either make the 13th CD much more Democratic by adding cities like Aurora and Joliet, or they could fold it into the 6th CD of more conservative GOP Rep. Peter Roskam to make way for a new Hispanic-majority seat on Chicago's North Side.
Bobby Schilling, IL-17
Democratic legislators in the Land of Lincoln could embark on the ultimate takedown: combining Schilling and one of two neighboring Republicans, 18th-CD Rep. Aaron Schock or 16th-CD Rep. Don Manzullo, into a Democratic-leaning western Illinois district none of them may be able to win. If either scenario comes to fruition, Schilling could well be the underdog in a primary against the skillful Schock or the seasoned Manzullo. Then, the winner could be an underdog in a general election. At worst, Democrats will have succeeded in collapsing two Republican seats into one.
Jeff Landry, LA-03
Louisiana Gov. Bobby Jindal (R) made clear that he preferred a plan to dismantle Landry's 3rd CD, and he got his way. Louisiana's newly approved plan splits Landry’s political base four ways and forces him into an unappealing primary against GOP Rep. Charles Boustany, who would retain almost all of his current 7th CD. This was hardly a surprise: Many Louisiana insiders note the awkwardness of Landry, a freshman closely aligned with the tea party movement, representing the coastline and advocating for some of the largest public-works projects in the country.
Andy Harris, MD-01
Democrats' not-so-secret antipathy toward Harris, whom they see as an ideologue and an interloper on the Eastern Shore, will surely play a role in their new Maryland map. The smart bet is that Democrats will redraw the non-Eastern Shore half of the 1st CD to include many more Democrats, in cities such as Aberdeen and Annapolis. At a minimum, they could draw the Baltimore-based Harris, a Republican freshman, far out of the 1st CD. They also hope to smooth the road for Eastern Shore Democrat Frank Kratovil to come back to Congress.
Bill Johnson, OH-06
After routing five Democrats out of office in 2010, Republicans in slow-growing Ohio are victims of their own success and may need to throw one of their own on the altar. Johnson, who didn't earn the acknowledgment of the NRCC until late in the campaign but upset Democrat Charlie Wilson anyway, represents a narrow strip of the Ohio River Valley and may be the odd Republican out. Still regarded as a bit of a fluke within his own party, Johnson could find himself in a primary against either Rep. Jean Schmidt to the west or fellow freshman Rep. Bob Gibbs to the north.
For more about the redistricting battles, National Journal subscribers can check out Redistricting Central.