CHARLESTON, South Carolina (CNN) -- South Carolina primaries are all about the base. That's true for both parties.
For Republicans that means conservatives. It's the conservative firewall state, where George W. Bush put out the John McCain brush fire in 2000.
For Democrats, it means African-Americans, who make up about half of the voters in the South Carolina Democratic primary. The main reason the Democratic Party is allowing South Carolina to hold an early primary is to give African-American voters a bigger voice.
As a result, South Carolina could be crucial in the selection of the Democratic nominee, just as it has been for Republicans for many years.
Unlike the turmoil in the Republican contest, the Democratic race has been fairly stable all year. Sen. Hillary Clinton has maintained a lead in the national polls, with Sen. Barack Obama second and former Sen. John Edwards third. No other candidate has made double digits.
The Clinton campaign has been trying to surround its candidate with the aura of inevitability: "Face it, she's going to be nominated. Better get on the bandwagon now.''
The CNN-YouTube debate in Charleston, South Carolina, Monday night could look like seven against one: seven Democratic contenders trying to challenge Clinton as "The Inevitable" -- and competing with each other to become "The Alternative." Watch CNN's Candy Crowley explain how the questions for the debate will be selected »
The debate, hosted by CNN's Anderson Cooper, begins at 7 p.m. ET.
One way to challenge Clinton has been to criticize her as too cautious and calculating -- a "triangulator.'' It's the same complaint many liberals had about her husband.
Early in the year, it appeared that Clinton might be vulnerable to that line of attack on the Democrats' number one issue -- the war in Iraq. Sen. Clinton refused to apologize for her vote in 2002 authorizing President Bush to use force. At first, she was cautious about demanding a timetable for the withdrawal of U.S. troops.
Since then, however, Clinton has made sure to allow no daylight between herself and other Democrats on the antiwar issue. She voted against a troop funding bill that contained no troop withdrawal deadline. Her squabble with the Pentagon over withdrawal plans has burnished her credentials as an antiwar candidate.
She has also been helped by her husband's increasingly visible role in her campaign. As President Bush's popularity has collapsed, former President Clinton's popularity has grown, especially among Democrats.
Many Democrats remember the Clinton era as the Golden Age in contrast with the last six and a half years under Bush. There doesn't seem to be much lingering resentment over triangulation, welfare reform, free trade or Monica Lewinsky.
Barack Obama has discovered another way to challenge Hillary Clinton's aura of inevitability: cash. Obama edged ahead of Clinton in fundraising, making a powerful impression on Democrats, especially because he did it with so many small contributors. Obama appears to be leading a genuine grassroots movement that could take on the party establishment.
Democrats really have two front-runners, not one: Obama in fundraising, Clinton in the polls. Moreover, the national polls don't mean a great deal when there is no national primary.
In Iowa, Clinton and John Edwards are in a close race. An Edwards victory in Iowa would throw the Democratic race wide open. Clinton would then rely on New Hampshire to restore her frontrunner standing.
But an upset is possible there, too. Obama is doing well among New Hampshire Independents, who can vote in the Democratic primary. If Edwards were to beat Clinton in Iowa and Obama were to beat Clinton in New Hampshire, her aura of inevitability would be shattered. Then what would happen?
Then it would come down to South Carolina, where African-American voters could be the Clinton firewall. The latest CNN-Opinion Research Corporation poll shows Clinton with a solid 16-point lead among black Democrats in South Carolina (and a 14-point lead among all Palmetto State Democrats).
But Clinton is not the only candidate who does well with black Democrats in South Carolina. Obama does, too. He could be highly competitive with her for black votes, particularly if he wins the New Hampshire primary. African-Americans might suddenly become excited by the prospect of nominating one of their own.
Another scenario: Clinton and Obama could split the black vote in South Carolina. That might enable Edwards to win the Democratic primary, as he did in 2004. Edwards was born in South Carolina and was elected to the Senate from neighboring North Carolina. And the CNN poll shows Edwards nearly even with Clinton among white Democrats in South Carolina.
There is one other issue competitors could use to challenge Clinton's inevitability, namely, her electability. So far, no other Democrat has brought up Sen. Clinton's relatively high negatives among Republicans and Independents. But her campaign has issued a steady stream of polling reports showing she can be elected and Democrats seem convinced.
In CNN's poll, South Carolina Democrats believe Clinton has a better chance than Obama of beating the Republican candidate in 2008, 54 to 35 percent. African-Americans seem to worry more about Obama's electability than Clinton's. By more than two to one (63 to 29 percent), black Democrats say Clinton is more electable than Obama.
Will voters raise questions about Clinton -- or Obama's -- electability? That's something to watch for in the upcoming debate. E-mail to a friend