Sens. Hillary Clinton and Barack Obama face their high-noon showdown on Tuesday in Indiana and North Carolina: The results of those two primary elections could prove the decisive turning point of the long race for the Democratic Party's presidential nomination.

Abraham Lincoln famously said at the beginning of the U.S. Civil War that he wanted God on his side, but he had to have Kentucky. That's the way Clinton, D-N.Y., and Obama, D-Ill., feel about the Indiana primary.

Two national polls published Sunday and Monday showed how confused and unpredictable the outcome of the great race still is: A USA Today/Gallup Poll published Monday among Democrats and likely Democratic voters showed Hillary surging ahead of Obama nationally by 51 percent to 44 percent. That marked a dramatic reversal of fortune from just two weeks ago when the same pollsters found Obama 10 points ahead of Hillary. One-third of those polled said that the continuing and growing controversy over the Rev. Jeremiah Wright, Obama's pastor for 20 years, made them less ready to vote for him.

But on Sunday a CBS/New York Times poll came to an opposite conclusion, giving Obama a still-comfortable 12-point national lead over Clinton. Which to believe? Neither. The Indiana and North Carolina returns on Tuesday night will give the results that really matter.

Clinton is still struggling to keep her wildly erratic campaign alive. The most ominous trend for her over the past two weeks has been a slow but steady drift of superdelegates into Obama's camp. Clinton could probably survive a defeat at Obama's hands in North Carolina, because he has long been expected to win there. And in America's new South, racism is not remotely as strong an influence as traditional regional rivalries and resentments.

Thus, though Obama and Clinton are in many respects remarkably similar products of Chicago's raucous, corrupt, cynical and tough-as-nails Democratic Party machine, Clinton wears the personality of New York City, which is an albatross around her neck in the South. Obama has failed disastrously to connect with northern industrial white working-class blue-collar Democrats. But he has done a lot better among white liberal Democrat Southerners.

That leaves Indiana as absolutely crucial for both Clinton and Obama. Even Clinton's unexpectedly decisive victory in the Pennsylvania primary after a grueling six-week campaign did not tilt the sentiment of the Democratic Party establishment toward her. A remarkable number of even senior officials and party loyalists to her husband, former President Bill Clinton, defected to Obama during and after that campaign. She has to win, and win clearly, in Indiana, just to keep her campaign alive at all. If she loses, the pressure from the Democratic Party establishment for her to stand down could rapidly become overwhelming.

But Clinton's troubles could look minuscule compared with Obama's if he can't win in Indiana. The 2000 and 2004 presidential campaigns confirmed the new 21st century political reality that the Midwest and the big industrial states of the Northeast have replaced the South as the crucial swing regions that most often decide U.S. national elections. If Obama can't even win over the loyal Democrats of crucial Pennsylvania in a primary, how can he hope to carry the whole state come November?

For all the talk about Obama's charisma, his inspiration to the American people and the genuine widespread appeal he has had for idealistic young millennial generation Americans, the junior senator from Illinois remains a surprisingly untested lightweight when it comes to proving his pulling power even among the broad core support of his own party. He has only won one primary in a large industrial state, his native Illinois, and one in a smaller industrial state, Wisconsin. He could not beat Clinton in Ohio, California, Arizona, New York, Michigan or Florida, and those are all must-wins for the Democrats in November. And his Illinois victory was delivered to him by the venerable and mighty state party machine that has run Chicago since the days of Prohibition 80 years ago.

Illinois party bosses also have a reputation for building up smooth-talking, young, apparently clean and innocent reformers and propelling them onto the national stage, as long as they don't ask too many questions or cause any real embarrassment to business as usual in Chicago. And Obama, like Illinois governor and twice presidential candidate Adlai Stevenson half a century ago, has loyally followed his script and his orders.

However, beyond the Lost World of the Illinois Democratic machine, Obama has yet to prove he can win, even among his own party loyalists at all. If he can beat Clinton in Indiana Tuesday, after all the negative publicity Wright has brought down upon his head, then he will be riding the wave again and posed to sweep away Clinton. But if he loses, then the worries that he is a luftmensch -- a man of air without substance -- will grow, and not all the media buzz on his behalf can prevent it.