By Andy Matthews

Republicans have a good shot at adding to their majority in the Senate this year (they currently control 51 seats), thanks to the retirement of five southern Democrats and the fact that most of the competitive races are in states President Bush is likely to carry.

Here's a rundown of this year's competitive races. Incumbents are designated with an asterisk.

Alaska: Sen. Lisa Murkowski (R)* v. Tony Knowles (D)
The former governor Knowles presents Murkowski with a tough test, particularly because Murkowski was appointed to her seat by her father, the current governor. President Bush will carry the state easily, which is a plus for Murkowski, but this one will be very close.
Prediction: Murkowski

Arkansas: Sen. Blanche Lincoln (D)* v. Rep. Jim Holt (R)
Either Asa Hutchison or Mike Huckabee would have been a stronger GOP nominee than Holt, but both declined to enter the race. Lincoln will likely retain her seat, though having Bush on the ballot should make it interesting, as the president figures to carry Arkansas.
Prediction: Lincoln

California: Sen. Barbara Boxer (D)* v. Bill Jones (R)
Boxer is vulnerable, but Jones, the former California Secretary of State, likely isn't a strong enough candidate to defeat her. Arnold Schwarzenneger's ascendency has no doubt galvanized California Republicans, but the state still leans heavily to the left, and John Kerry is likely to carry it this year.
Prediction: Boxer

Colorado: Pete Coors (R) v. State Attorney General Ken Salazar (D)
This is one of the more intriguing races in the country this year, and could very well be one of the closest. When Republican Ben "Nighthorse" Campbell announced his decision not to seek re-election, the party turned to popular Governor Bill Owens, hoping he'd run. When Owens said no, the GOP turned its eyes toward Rep. Bob Schaffer. But in yet another twist, the brewer Coors jumped in and beat Schaffer in the Republican primary. He'll face Salazar, who should not be taken lightly, even in this pro-GOP state. Polls show a tight race right now.
Prediction: Salazar

Florida: Betty Castor (D) v. Mel Martinez (R)
This race -- to fill the seat being vacated by retiring Democrat Bob Graham -- could be the most interesting in the nation. Martinez, the former HUD Secretary, won a bitter primary, and it will be interesting to see whether that hurts him. Castor, the former state education commissioner, is a formidable foe. Bush is likely to carry Florida, so that could be an additional factor.
Prediction: Martinez

Georgia: Rep. Denise Majette (D) v. Rep. Johnny Isakson (R)
With Zell Miller (D) retiring, this is an open seat, and Isakson should win hands down. Georgia is one of the most solid GOP states in the nation, and Majette will be lucky to attract even 40 percent of the vote.
Prediction: Isakson

Illinois: Alan Keyes (R) v. State Sen. Barack Obama (D)
Republicans stood a decent chance of holding on to the retiring Pete Fitzgerald's seat, but then the whole Jack Ryan fiasco ruined their chances. Illinois is a pro-Democrat state, and Obama is an impressive candidate who likely would have beaten Ryan anyway. With Keyes on the ballot, he'll win in a landslide.
Prediction: Obama

Kentucky: Sen. Jim Bunning (R)* v. State Sen. Daniel Mongiardo (D)
Bunning may have been vulnerable this year, but Mongiardo isn't a strong candidate and faces an uphill battle to knock off the incumbent.
Prediction: Bunning

Louisiana: Rep. Chris John (D), State Treasurer John Kennedy (D), State Rep. Arthur Morrell (D) and Rep. David Vitter (R)
These four, all vying to replace retiring Democrat John Breaux, will face off on election day, with a runoff to follow if no candidate wins a majority of the vote. The only one with a realistic chance to win outright is Vitter, the only Republican in the field. Odds are this will go to a runoff between Vitter and John, where the Republican should have the edge in this pro-GOP state.
Prediction: Vitter in a runoff

Missouri: Sen. Kit Bond (R)* v. Nancy Farmer
Democrats thought Bond was vulnerable this year, but Farmer trails badly in the polls. Kerry's decision to abandon Missouri won't help her.
Prediction: Bond

Nevada: Sen. Harry Reid (D)* v. Richard Ziser (R)
Rep. Jim Gibbons would have been a strong GOP candidate, but he stayed out of the race. Ziser is a much weaker candidate, and Reid will likely hold on to his seat.
Prediction: Reid

North Carolina: Erskine Bowles (D) v. Rep. Richard Burr (R)
For a while, this one seemed likely to go as a missed opportunity for the GOP. Bowles, the former Clinton Chief of Staff, lost badly to Elizabeth Dole in a Senate bid two years ago, and is now trying to win the seat being vacated by John Edwards. North Carolina leans to the right, but Burr initially had a tough time in the polls. He's since turned things around, and should be boosted by Bush's presence on top of the ticket.
Prediction: Burr

Oklahoma: Rep. Tom Coburn (R) v. Rep. Brad Carson (D)
Coburn, a rock-solid conservative, should benefit from both the state's rightward tendencies and the fact that Bush will carry the state handily. Democrats consider this race -- which will determine who replaces retiring Republican Don Nickles -- within their grasp, but it's hard to see Carson pulling it out.
Prediction: Coburn

Pennsylvania: Sen. Arlen Specter (R)* v. Rep. Joe Hoeffel (D)
After surviving a major scare in the primary, courtesy of Pat Toomey, the moderate Specter won't have any trouble beating back Hoeffel, who has proved to be a disappointment.
Prediction: Specter

South Carolina: Inez Tenenbaum (D) v. Rep. Jim DeMint (R)
In a race to fill the seat of retiring Democrat Fritz Hollings, DeMint has a definite edge over Tenenbaum. South Carolina has grown more and more pro-GOP in recent years, and this is yet another case where President Bush's name on top of the ticket will help the Republican even more. In DeMint's case, he won't need it.
Prediction: DeMint

South Dakota: Sen. Tom Daschle (D)* v. John Thune (R)
The former Rep. Thune is running neck and neck with the Democrats' leader in the Senate, and Republicans are no doubt salivating at the thought of sending this obstructionist home. I'm going to bet that Bush's presence on the ticket in this heavily Republican state will be just enough to push Thune over the top.
Prediction: Thune

Washington: Sen. Patty Murray (D)* v. Rep. George Nethercutt (R)
Murray is vulnerable this year, and had Rep. Jennifer Dunn, the Republicans' first choice, entered the race, this seat might have switched hands. Nethercutt is a decent candidate, but he comes from the eastern part of the state, which is usually a disadvantage in statewide races here.
Prediction: Murray

Wisconsin: Sen. Russ Feingold (D)* v. Tim Michels (R)
Feingold will most likely hold on here, but this race may offer the best chance for a real surprise. The Democrat isn't all that populer, and Michels, a veteran and businessman, had a lot of money to pour into the race. Wisconsin is likely to go for Bush, so watch this one closely.
Prediction: Feingold

The remaining incumbents -- Shelby (R), McCain (R), Dodd (D), Inouye (D), Crapo (R), Bayh (D), Grassley (R), Brownback (R), Gregg (R), Schumer (D), Dorgan (D), Voinovich (R), Wyden (D), Bennett (R) and Leahy (D) -- should win easily.

The result? A net gain of four seats for the Republicans, increasing their total number of Senate seats to 55.

Andy Matthews is the editor of rightturnonly.com.