INDIANAPOLIS -- Barack Obama's success so far in this campaign is a puzzle. How is it that a youngish first-term senator with so many disadvantages -- a slight resume, a foreign-sounding name, an exotic background, a professorial manner, a thoroughly liberal voting record, and a skin color unlike any previous president -- has come so far, and even leads in national polls with less than two weeks to go?

He does have some things going for him, of course: his rhetorical skill, his unflappability and not least of all a financial crisis that reflects badly on the party occupying the White House. But none of those explains how he managed to defeat a daunting Democratic rival and outshine an inspiring war hero with demonstrated crossover appeal. If you had written the story as fiction a few years ago, publishers would have rejected it as grossly outlandish.

But the implausibility of the occasion is no deterrent to the 35,000 people who have turned out this weekday morning to see one of the few Democratic presidential candidates to imagine he might carry the staunchly Republican state of Indiana.

It is a racially mixed audience, and I meet a variety of participants, including a white factory worker, a black pharmacy technician, a group of white teens from Illinois in blue Future Farmers of America jackets and a black ex-Marine who teaches middle school. There is also a quartet of lively middle-aged women -- two white, two black -- who, after dancing happily to the warmup music, christen themselves the Michellettes.

And what did they hear from the man they came to see? Much of Obama's address consisted of standard campaign riffs, most of which could be delivered just as well by his opponent, on timeworn topics: the plight of the middle class, the need for tax relief, the unfairness of our health care system and the failure of economic policies that -- can you guess? -- "put Wall Street before Main Street."

But wait long enough, and you hear the indispensable passage, the one that transcends everything else he says. "There are no real and fake parts of this country," Obama declares. "We are not separated by the pro-America and anti-America parts of this nation -- we all love this country, no matter where we live or where we come from." America's veterans, he says, "have fought together and bled together and some died together under the same proud flag. They have not served a Red America or a Blue America -- they have served the United States of America."

From the moment he vaulted into national consciousness with his inspiring speech at the 2004 Democratic National Convention, this theme has lain at the heart of his approach and his appeal. "We worship an awesome God in the Blue States, and we don't like federal agents poking around in our libraries in the Red States," he reminded us then. "We coach Little League in the Blue States and yes, we've got some gay friends in the Red States."

It is a message of fundamental unity and good will, at a time when politics often resembles Henry Adams' mordant description: "the systematic organization of hatreds." And it has worked especially well for Obama for several reasons. One is that, as the son of an African father and a white, Kansas-born mother, he embodies the diversity of America.

Another is that it contrasts so starkly with the message of the opposing camp. You have Rep. Robin Hayes (R-N.C.) saying "liberals hate real Americans that work and accomplish and achieve and believe in God." You have Rep. Michelle Bachmann (R-Minn.) suspecting the Democratic nominee is "anti-American." You have Sarah Palin saying she loves "what I call the real America [the] very pro-America areas of this great nation."

It's a strategy of fear and division, and it seems to be failing because Obama is not very scary and because the things that bind us together really are more powerful than the ones that push us apart.

Which brings us to the most important reason for the success of his message: It touches a chord that resonates not just across races and regions, but across more than two centuries of the republic's history. Whatever his errors, Obama's campaign and the followers it has inspired remind us of the essential meaning of America, captured in the motto adopted by the Founders: E pluribus unum. Out of many, one. Not: Out of many, two.