COLUMBIA - Democrat Inez Tenenbaum and Republican Jim DeMint have boiled down their race for the U.S. Senate to a single argument: My opponent wants to raise your taxes.

Their television commercials make it sound simple.

Tenenbaum warns of DeMint's "new 23 percent federal sales tax on just about everything we buy." A DeMint commercial says "Inez Tenenbaum supported the largest tax increase in state history, almost a billion dollars a year."

Both candidates' ads oversimplify to the point of being misleading. What's more, Tenenbaum and DeMint are now spending almost all their time arguing the pros and cons of an idea that probably will never be adopted.

Here are the facts:

• DeMint, a three-term U.S. House member, last year joined 53 House Republicans in sponsoring a bill, H.R. 25, that would abolish all federal income taxes and other payroll taxes and replace them with a 23-cent national sales tax. Part of the sales tax would be rebated to people in monthly checks averaging about $400 per family. DeMint has also introduced a bill to create a nonpartisan commission to study alternatives to the income tax and come up with a replacement.

• Tenenbaum, South Carolina's elected state superintendent of education, in 2003 came out in favor of a 2-cent hike in the state sales tax for the public schools. That idea was later folded into a proposal for the state to assume all public school operating costs, thereby cutting most people's local property tax bills about in half.

The 23-cent sales tax has become the consuming issue of the Senate campaign because Tenenbaum, who is behind in the race, has made it so. For the last month, it has been virtually all she has talked about, in her commercials and in her daily campaign stops.

DeMint reacted by accusing Tenenbaum of lying, while branding her the real tax-lover in the race.

At the time Tenenbaum called for new taxes, South Carolina was in the midst of a budget crisis and the state's public schools were facing a cut in the per-pupil allocation -- the base amount that goes mostly toward teacher salaries.

During a rally on the State House steps in April 2003, Tenenbaum said that without more state money, thousands of teachers would have to be laid off. She said that she and some lawmakers were working on a plan for a 2-cent increase in either state sales tax, the cigarette tax, the gasoline tax, or the beer and wine tax.

The final plan, which would raise the sales tax by 2 cents while lowering property taxes, was presented to the legislature later in 2003 by then-House Republican leader Rick Quinn and Democratic Rep. Vincent Sheheen. So far, lawmakers have failed to act on it, and Quinn's defeat in the June 2004 Republican primary has put the plan on hold. As for DeMint's tax proposal, economic experts say that while replacing the nation's complicated tax laws with a sales tax or a flat tax, may sound attractive, it is loaded with unknowns. Among those is whether it could really pay for all the things government spends money on.

"His supposed goal of simplifying the tax structure by a massive overhaul is a fool's errand; it's not going to happen," said University of South Carolina economics professor James Bradley, a former chairman of the state's Board of Economic Advisers.

Political observers say Democrats in Congress would never allow a sales-tax bill to go through because they think it would shift the tax burden onto lower-income people.

"It's an interesting idea from the standpoint of theory, but I can't see it ever going through," said Danielle Vinson, a political science professor at Furman University in Greenville.

Vinson said she suspects that DeMint realizes his sales tax idea is far-fetched. "On a lot of the ideas that I've heard him espouse over the last six years, I think he's just someone who likes to consider new options, even some that aren't terribly realistic."

Both sides say their polls show a closer race than two weeks ago, though their numbers vary greatly. While Tenenbaum's handlers say she has pulled to within the poll's 4 percentage points margin of error, DeMint's campaign manager, Terry Sullivan, says DeMint still holds a 9-point lead.

Political observers say Tenenbaum appears to be getting some advantage from the tax issue, but they say she will need more than that if she hopes to win in this Republican-leaning state. The Senate seat that Tenenbaum and DeMint are contesting is held by Democrat Ernest "Fritz" Hollings, who is stepping down after 38 years.

"My guess is that Tenenbaum could gain some traction attacking this (tax) because she's oversimplifying his plan dramatically," Vinson said. "Her ads leave out the rebates, and they don't mention the income tax going away at all."

Vinson said DeMint will have difficulty explaining his plan -- as his latest TV commercial, released Friday, attempts to do -- "just because his plan isn't easy to summarize in 30 seconds. She can easily get through to people in 30 seconds saying, `You're going to be paying 23 percent on everything you buy.' "

But, said Earl Black, a political science professor at Rice University in Houston and an authority on Southern politics, "It's pretty difficult to take a single issue in a state and really make that an issue that changes a lot of minds and a lot of votes in a short period."

He said, "Most people are going by the big symbols of `R' and `D.' Democrats are viewed more as the party of big government and hence, additional taxation. It's very difficult for an individual candidate to change those perceptions that have come out of national politics for a long, long time."