COLUMBIA, S.C. - South Carolina has become a must-win state for Barack Obama.
Whatever the outcome of Saturday's Democratic presidential primary here, the Illinois senator has the money and the organization to compete in the nearly two dozen states voting Feb. 5.
But as his first and only victory in Iowa on Jan. 3 slips further into history, his strategists concede that Obama badly needs to demonstrate broad enough support to slow Hillary Clinton's progress toward the nomination.
Having trailed her in popular votes in both New Hampshire and Nevada, where he was favored, Obama finds himself more in need of help than he perhaps expected from the voters here.
This state offers him many advantages he will not enjoy automatically when the competition moves to California, New York, New Jersey and other delegate-rich states next month.
The black vote is a larger percentage of the Democratic electorate here - perhaps half the total - than in any of those states, and even Clinton supporters credit Obama with having the best field organization on the ground. Clinton has switched her South Carolina leadership several times, while Obama has had steady and impressive local management.
This is also the state that John Edwards won in 2004 - and perhaps the last place where the native son can be expected to siphon off a significant number of white votes this year, simplifying the math for an Obama victory in a state where racial polarization often prevails.
For all these reasons, anything other than victory for Obama on Saturday would represent a significant setback to his long-term prospects, while Clinton has built-in alibis for a possible loss.
The stakes may explain why tensions became so obvious during the Monday night debate in Myrtle Beach, with Clinton and Obama accusing each other of distorting the record and falsifying their own voting histories.
Their exchanges were personal and angry. He referred to her as a corporate lawyer who had served as a director for Wal-Mart, a company with an anti-union reputation. She shot back that he had been a lawyer for a reputed Chicago slumlord. Any thought that these two might someday team up as a Democratic ticket vanished into the night.
Edwards seemed stunned by the ferocity of the other two, but took advantage of the situation by landing some punches of his own on both. He sided with Clinton on health care, but reinforced Obama's contentions on campaign finance, special interests and Social Security, only to switch and join Clinton in questioning why Obama had voted "present" so often in the Illinois Legislature.
No one came out unscathed, but Edwards probably fared best, raising the possibility that he could split the white vote with Clinton and, ironically, thereby help Obama.
But all that is down the road from South Carolina. For now, Clinton and her husband, the former president, have gotten inside Obama's head and rattled his composure. Obama seemed unusually defensive in his speech here Sunday evening, launching the final burst of campaigning in the state.
He deviated from his standard "time for a change" and invocation of hope to deliver a point-by-point rebuttal to the arguments that have come from the Clinton campaign since they recognized his threat in Iowa.
He ripped Clinton by name for her hypocrisy in supporting a bankruptcy bill and then saying she hoped it would not become law. That, he said, is the kind of double-talk his critics would like him to learn - but he said he scorns.
He accused her also of distorting his position on Social Security, by describing his support for raising the ceiling on payroll taxes above the current $102,000 a year as "a trillion-dollar tax increase." He said that it would hit only the top 4 percent of earners.
He also sought to dispose of complaints from both Clinton and Edwards about his favorable comments to a Nevada newspaper about Ronald Reagan - disclaiming any idea that he embraced Reagan's economic or social policy and arguing that he wanted only to emulate Reagan's ability to win support from voters aligned with the other party.
While he was on his defensive spiel, Obama also urged people to ignore "crazy" rumors that he was a Muslim, not a Christian, or ever failed to recite the Pledge of Allegiance or take his oath to uphold the Constitution.
Many of those same points came up again in the Monday night debate, where the audience seemed sympathetic to Obama's answers. He has to hope that he is not misreading the South Carolina electorate, because a rejection here would be bad news indeed for what looms ahead.
E-mail nationally syndicated columnist David Broder at email@example.com.