Unlike some, I continue to rate the South Carolina Senate contest as leaning Republican. Others, including most Democrats, argue it’s a tossup. Given that, I thought I should explain my reasoning for handicapping the contest as I do.

First, as I have already written and said many times, Democratic Senate nominee Inez Tenenbaum is an excellent candidate. She is outgoing, energetic, articulate and personable. Whether in an interview with a couple of reporters or on a stage at a garage in Columbia, S.C., during the weekend of the first Democratic presidential debate, Tenenbaum has proven her skills and appeal. [IMGCAP(1)]

Tenenbaum’s election as state commissioner of education demonstrates that she can attract votes. And because she is a statewide elected official, her name recognition in South Carolina is considerable.

Early public polling has put Tenenbaum ahead of most of her potential general-election opponents, and her early fundraising has been good. She collected more than $900,000 in the first three months of this year, ending March with $1.2 million in the bank.

Finally, Tenenbaum stands to benefit from the fact that the Republicans must undergo a multicandidate primary and, almost certainly, a runoff before they can even focus on Tenenbaum in the general. By contrast, Tenenbaum faces no primary opposition, allowing her to husband her resources for the fall.

If this was the end of the story, I wouldn’t rate Tenenbaum’s race merely as a tossup. I’d call her the favorite. But it’s not the end of the story.

In my view, South Carolina’s partisan fundamentals are clear: The Republicans begin with a considerable advantage in any statewide federal contest.

The GOP currently controls both chambers of the state Legislature and the governorship, plus four of the state’s six U.S. House districts. The state’s attorney general, secretary of state, comptroller, adjutant general and state agricultural commissioner are also Republicans. Tenenbaum and state Treasurer Grady Patterson are the only Democrats holding statewide office.

The last Democratic presidential candidate to carry the state did so 28 years ago: Jimmy Carter, who had been governor of next-door Georgia. Democrat Fritz Hollings won a special election in 1966 and then went on to win six re-election contests. But Hollings’ recent victories rested on his incumbency and his ability to rake in money from the business interests he oversaw as the top Democrat on the Senate Commerce, Science and Transportation Committee. And even then he did not break 53 percent in either of his last two re-election bids.

In the meantime, the divisions now showing on the Republican side are exaggerated, because the party is in the middle of a primary.

At this point, Rep. Jim DeMint is more focused on defeating former Gov. David Beasley for the nomination than in defeating Tenenbaum this fall. Businessman Thomas Ravenel is more interested in pointing out his differences with DeMint and Beasley than with contrasting himself with Tenenbaum. And former state Attorney General Charlie Condon is focused more on overtaking two of the other Republicans in the race than he is in overtaking the Democratic nominee.

But after the runoff is over — and after the intraparty wounds heal — the GOP will benefit from having a single standard-bearer. That will automatically change how some Palmetto State voters view the Senate race.

Elections are decided by candidates, campaigns and specific circumstances, such as the state of the economy, specific issues of local interest, the public’s mood and other races on the ballot. But the underlying context of every race includes partisanship and ideology. In South Carolina, both of those factors favor the GOP, even if it’s fashionable to say that the Republican advantage in the state is overrated.

There are always exceptions, such as both Dakotas, where Democrats have held on to both Senate seats in otherwise Republican environments thanks to a combination of voters’ pro-spending sentiment and incumbency. And some states are so evenly divided that neither party has a clear advantage.

But all things being equal, Democrats will tend to win Senate races in Massachusetts while Republicans win them in Wyoming. And in South Carolina, the GOP grip has become strong enough that a credible Republican open-seat nominee begins with a significant advantage. Remember, Al Gore lost the state to George W. Bush by 16 points, and then-Rep. Lindsey Graham (R) beat the folksy and much-hyped Democratic Senate hopeful Alex Sanders by a comfortable 10 points two years later.

I expect this year’s Senate race to be closer than that, with the margin ending up somewhere in the middle or low single digits. But the dynamics are such that the Republican nominee can afford to lose some of the “normal” GOP vote — some of the voters who supported Graham and Bush in the past — and still win.

By late September we should all have a better idea about whether the GOP is united enough behind its nominee to win; whether the Republican candidate has enough strength to take advantage of his party’s edge in the state; and whether Tenenbaum’s personal appeal is strong enough to overcome her partisan disadvantage.

But until the evidence convinces me that Tenenbaum is just as likely to win the race as she is to lose it, I’ll go with the state’s fundamentals every time. Four months from now, this race could look very different. For now, though, it’s still slightly uphill for the Democrat.

Stuart Rothenberg is editor of the Rothenberg Political Report.