INCUMBENT POSSIBLE CANDIDATES e>
ArizonaGov. Jan Brewer (R) state Attorney General Terry Goddard (D)*
The untested Brewer, who was Arizona's secretary of state until her predecessor joined Obama's Cabinet, has fought with her party over a proposed tax increase.
Gov. Bill Ritter (D) former Rep. Scott McInnis (R) state Senate Minority Leader Josh Penry (R) e>
Low approval ratings, controversy over his appointing Sen. Michael Bennet, and the recession place Ritter in Republican crosshairs.Sen. Michael Bennet (D) former Lt. Gov. Jane Norton (R) Aurora City Council member Ryan Frazier (R) Weld County District Attorney Ken Buck (R) ftate House Speaker Andrew Romanoff (D) e>
Bennet, an untested appointee with low name identification, faces a possibly bruising primary against an experienced candidate and the likelihood of a tough general election campaign if he wins the primary.Rep. Betsy Markey (D) State House Minority Whip Cory Gardner (R) e>
Markey has been surefooted but might face a tough challenge in this Republican-leaning, exurban district.
IdahoRep. Walt Minnick (D) Iraq veteran and McCain Nevada campaign director Vaughn Ward (R) e>
Minnick benefited from a split Republican Party in 2008; he won't have the same advantage this time in a strongly Republican district.
NevadaGov. Jim Gibbons (R) Clark County Commission Chairman Rory Reid (D)* Las Vegas Mayor Oscar Goodman (D)* former federal Judge Brian Sandoval (R) former state Sen. Joe Heck (R) North Las Vegas Mayor Mike Montandon (R) e>
A series of scandals and a collapsing state economy have left Gibbons facing dismal poll ratings, a tough primary, and a potentially strong Democratic candidate.Sen. Harry Reid (D) businessman Danny Tarkanian (R) state GOP Chairwoman Sue Lowden (R)* state Sen. Mark Amodei (R) former state Rep. Sharron Angle (R) e>
Reid's poor poll numbers have Democrats fearing a repeat of Senate Democratic Leader Tom Daschle's 2004 defeat.Rep. Dina Titus (D) banker John Guedry (R)* e>
Titus won in 2008 with only 47 percent of the vote and could face another tough race in this centrist district based in suburban Las Vegas.
New MexicoGov. Bill Richardson (D) Lt. Gov. Diane Denish (D) (term-limited) former Rep. Heather Wilson (R)* Dona Ana County District Attorney Susana Martinez (R) state Rep. Janice Arnold-Jones (R) businessman Doug Turner (R) e>
Denish is the front-runner, but Republicans have strong options.Rep. Harry Teague (D) former Rep. Steve Pearce (R) e>
Former oilman Teague took a risk by supporting the Democrats' bill to limit climate change; his likely challenger is Pearce, who ran for the Senate rather than re-election in 2008.* Possible but undeclared candidates Compiled by e>
National Journal Researcher Cameron Joseph.