Come Election Night, the biggest nail-biter of all might not be the presidential race but the battle for control of the Senate. Five retirements by Democratic Senators in the Deep South gave the GOP hope for extending its barely workable majority of 51-48 (with a lone independent who leans Democratic).

But several of those Southern seats have proven more competitive than first thought, and Republicans got hit with a few retirements of their own. Now the experts don't know what to expect. Predictions range from a Democratic takeover to a net gain of three for the GOP.

For Election Night parties, here's the statistic to keep in mind: If Republicans win three of the five Southern seats (N.C., S.C., Ga., Fla., and La.), there's no way for Democrats to do better than a tie.

South Carolina

(open Democrat)

South Carolina is a state about as conservative as they come-yet GOP Rep. Jim DeMint is struggling in his bid to fill Fritz Hollings's open Senate seat. Mr. DeMint attracted national ridicule by saying that gays and unwed mothers should not be allowed to teach in public schools. An Oct. 17 candidate face-off turned into a mini-referendum on the issue, with Mr. DeMint (sort of) apologizing for the statement about a half-dozen times.

Mr. DeMint's opponent, state Education Superintendent Inez Tenenbaum, has portrayed herself as a pro-military, pro-family independent. Her yard signs don't mention her party affiliation, and she refused to be seen onstage during a September rally for V.P. nominee John Edwards.

Mr. DeMint maintains a narrow lead in a race that has become the most expensive in S.C. history.

North Carolina

(open Democrat)

Of the five Southern Senate seats vacated by retiring Democrats, the national party thought North Carolina represented its best chance for a hold. Now they're not so sure. After months of double-digit leads in the polls, former Clinton chief of staff Erskine Bowles has watched his race narrow to a dead heat. His opponent, GOP Rep. Richard Burr, performed well in their lone debate and won credit with many farmers for the Oct. 11 passage of a $10 billion tobacco buyout plan.

A more competitive presidential race might have boosted Mr. Bowles, but Mr. Kerry has all but pulled out of North Carolina despite his running mate's "favorite son" status.

Georgia

(open Democrat)

Retiring Democratic Sen. Zell Miller already votes with the GOP, and now the party has a near-lock on replacing him with a full-fledged Republican member. GOP Rep. Johnny Isakson leads his Democratic challenger, Rep. Denise Majette, by nearly 20 points, and almost no one rates the state as a tossup. Still, Democrats have a lock of their own in Illinois, so flipping Georgia to the Republicans will merely maintain the status quo.

Louisiana

(open Democrat)

Thanks to Louisiana's bizarre electoral system, if GOP Rep. David Vitter can't reach 50 percent of the vote on Nov. 2, control of the Senate might not be determined until a December runoff. Polls show Mr. Vitter at nearly 45 percent, more than his three Democratic opponents combined. National Democrats are pouring millions of dollars into the race to ensure that they get a chance to go mano a mano against the two-term Republican lawmaker. But Democratic voters are almost evenly divided, making it harder to unify the party in time for a runoff election.

Oklahoma

(open republican)

It's anybody's guess who's really leading in the race to succeed retiring GOP Sen. Don Nickles. One mid-October poll had Democratic Rep. Brad Carson up by 2 points, while another favored former Republican Rep. Tom Coburn by 5. But all the pollsters agree: The race is within the margin of error and anything could happen.

In a solidly Republican state, Mr. Coburn's bitter struggle to hold the seat is a testament to negative campaigning by the Democrats and infighting among the Republicans. His best chance to break out of the deadlocked race will come in a series of three debates Oct. 21-27.

Colorado

(open republican)

President Bush might seem to have enough on his plate these days, but on Oct. 11 he took the time to headline a fundraiser for GOP Senate candidate Pete Coors-a sign of just how badly the Republicans need to hang on to this seat. After leading by 11 points in an early October Gallup poll, Democratic Attorney General Ken Salazar saw his lead shrink to just 1 point in another Gallup poll released Oct. 18.

Still, it's a tough seat for the GOP. The party's national Senate elections committee is spending just $550,000 on TV ads in the campaign's final month, compared to more than $2 million by the Democratic committee-a possible sign that Republicans are preserving their capital for races they deem more winnable.