In the last ten years, Republicans have had twice as many Southern Senate incumbents get tossed out of office by the voters. So why does the GOP have a 20-8 advantage over Democrats in 14 Southern states? It’s because Republicans have overwhelmingly won open seat contests.

I’m sure the GOP is fretting about having to defend at least four Southern Republican Senate seats in 2010 (so far), while no Southern Senate Democrat is likely to step down. But Republicans have had a pretty good track record defending their own open seats.

Republicans were able to hold onto Fred Dalton Thompson’s seat in Tennessee in 2002, with former Governor Lamar Alexander. In Texas, Attorney General John Cornyn hung on to Senator Phil Gramm’s job. Both Carolinas featured retirements that year (by Strom Thurmond and Jesse Helms) but Congressman Lindsey Graham and ex-Senator Robert Dole’s wife Elizabeth didn’t let those seats get away that year. Then in 2004, Congressman Tom Coburn did the same for Oklahoma when Don Nickles had enough of the United States Senate. In 2006 Chattanooga Mayor Bob Corker kept Tennessee in the GOP column after Bill Frist retired. Additionally, Congressman Roger Wicker kept Trent Lott’s seat in GOP hands in Mississippi in subsequent years.

In only two cases did a retiring Republican lead to a Democratic Party takeover. One occurred in 2000 as Connie Mack gave way to State Insurance Commissioner Bill Nelson in Florida. The other happened last year when former Governor Mark Warner replaced GOP Senator John Warner in Virginia. But a 77.8 percent success rate in GOP open seats should calm some Republican fears about 2010 and those Republican retirements.

On the other hand, the Grand Old Party has boosted their Southern membership at the expense of Democrats. The Democratic Party debacle occurred in the 2004 election, as five Democratic Party seats went Republican. This occurred in Georgia (where Congressman Johnny Isakson replaced Senator Zell Miller), South Carolina (where Congressman Jim DeMint filled in Senator Ernest Hollings Jr.’s spot), North Carolina (where Congressman Richard Burr took over Senator Jonathan Edwards’ post), Louisiana (where John Breaux’s Democratic seat flipped to Congressman David Vitter) and Florida (where ex-Housing Secretary Mel Martinez was chosen as Senator Bob Graham stepped down).

Republicans have thus won 12 open seat contests, losing two, for an amazing +10 margin in the South and an 83% success rate in these races. But how can Republicans ensure their success rate continues? One might involve picking members of Congress for their nominees. In open seat contests, Republican representatives went 7-1, with only Congressman Bill McCollum losing in Florida in 2000. Contrast that with the record of statewide officials, who are only 2-1 for the GOP in open seat contests, with Jim Gilmore losing in 2008 in Virginia. Those without experience in either realm did go 3-0, but Dole and Martinez only lasted a single term (with Corker having yet to complete his first term in office. Therefore, the GOP should look first for nominees with congressional experience, like Congressman Roy Blunt who is seeking Kit Bond’s open seat in Missouri. In Texas, wooing Congressman Joe Barton into Senator Hutchison’s race wouldn’t be a bad idea. But regardless of the nominee, the prospects for Democrats to pick up any of these four Southern Senate seats don’t look very promising.