There is not much doubt about which party will lead in the South. Back in 1966, the South elected only 29 Republican House members (including future President George H.W. Bush) to 95 Democrats. Democrats led in the popular vote there by a 63 percent to 36 percent margin.
In 1992, as Bush was getting thumped in the presidential election, Republicans won a higher percentage of the House popular vote in the South than the North for the first time since Reconstruction. In 1994, they carried the popular vote in the South by 55 percent to 43 percent. They have carried it ever since, even in 2008, when Barack Obama brought out unprecedented numbers of black voters in the South.
Republicans currently hold an 82-to-63 edge in Southern House seats, with eight Democratic-held seats rated likely or leaning Republican by realclearpolitics.com and another 11 Democratic-held Southern seats rated as toss-ups. And 15 more are in play, rated as likely or leaning Democratic.
So Republicans could easily gain 20 seats in the South. But they could gain even more in the North if current numbers hold up.
In 2008, Democrats won the popular vote in the North by 57 percent to 40 percent -- roughly comparable to their lead way back in 1964, the year of Lyndon Johnson's landslide.
If the popular vote in the North should turn out to go narrowly Republican, as it did in 1966, it could be disaster for Democrats. They lost a net 38 seats in the North that year, when they held just about as many seats Northern seats as now. Not a happy scenario for Democrats. But not out of the realm of possibility.