WASHINGTON — In February 1981, at the small, mostly white college he was attending in Los Angeles, 19-year-old Barack Obama tried something that shaped the course of his life.

He gave a speech.

Like many students of that era, the sophomore was drawn to the South African divestment movement, which demanded that college trustees drop institutional investments that supported the racial segregation system known as apartheid. Obama's role at the Occidental College rally that warm winter day was to grab the crowd's attention, then be whisked off by students in paramilitary costumes.

"He was so composed in his arguments that I think after that speech a lot of people wondered, 'Who is that guy and why haven't we heard more from him?' " recalled Rebecca Rivera, a classmate.

That debut speech was a turning point; it set a template for revealing a rare talent.

Nearly a quarter-century later, another Obama speech, this one at the 2004 Democratic National Convention, transformed him into an American political phenomenon. It launched him from being an obscure state lawmaker into a celebrity U.S. senator from Illinois and gave him a springboard to become a challenger for his party's 2008 presidential nomination.

While Democratic and Republican rivals campaign on their military heroism, governing resumes, private-sector success or White House ties, what sets the 46-year-old Obama apart most is how he engages audiences, physically and emotionally. His presence helps him transcend his biracial background.

He seems to hug and shake a crowd at once. On the campaign trail, he has a crisp, resonant voice combined with an easy, self-effacing manner. Tall, slim, with exceptionally long fingers, he juxtaposes a physical sense of calm with disarmingly emotional strings of words. His presence lets him lift a vague stump speech about hope into something that seems much weightier, at least in the moment.

Hearing his own voice that day at Occidental seemed to spark Obama's political awakening.

"I knew I had them (aspirations), that the connection had been made," Obama wrote of that day in his memoir "Dreams from My Father." "I really wanted to stay up there, to hear my voice bouncing off the crowd and returning back to me in applause. I had so much left to say."

FROM HAWAI'I TO POLITICS

Obama soon followed a path to politics. He transferred within months to Columbia University. He spent a few years as a community organizer in Chicago. He joined a church. He went to Harvard Law School, where he became the first black president of the Law Review. Next came a do-good job at a civil rights law firm and work as a constitutional law professor.

Election to the Illinois Senate followed, then a failed bid for the U.S. House of Representatives and a shoot-the-moon campaign for an open U.S. Senate seat. He won, helped greatly by his opponents' flameouts.

Finally came the invitation to give "the speech" in 2004, after Democratic presidential nominee John Kerry determined that Obama projected the right image.

None of this was predestined for a man with Obama's odd upbringing.

"Barry," as he was known into his 20s, was born and mostly grew up in Hawai'i, minus four years in Muslim Indonesia with his mother's second husband.

His white Midwestern mom and her parents reared him and sent him to Punahou School in Honolulu. But he yearned for a closer connection to his African father, who left when Obama was 2. He met his father only once after that and knew him mostly as a mythical figure in Kenya, yet he still identified himself as black.

After the campus divestment campaign, social justice, especially for black Americans, became his cause and guided his life choices.

Judson Miner, who heads the liberal Chicago civil rights firm that hired Obama after Harvard, said the first time he had lunch with his recruit, he was so struck by Obama's thought process and by how he drew others into conversation that, "I told my wife I just had lunch with one of the most extraordinary people I'd met."

"This was a guy who was interested in having an impact with things," Miner said. "I think he was really wrestling with, how can you be most effective? As a lawyer? In some other role? We never talked about politics, but I wasn't surprised when he came to me a few years later and said there was this opportunity in the state Senate."

Miner enthusiastically supports Obama's presidential bid.

"If he had a fault, which I guess sometimes manifests itself on the campaign trail, he instinctively appreciates all the nuances of things," Miner said. "He's decisive, but that processing involves wrestling with these things a little bit. And sometimes that's not a good trait for a politician."

CRITICS' BARBS

Obama's critics see bigger flaws in his judgment, which they chalk up to a combination of inexperience and sanctimony.

One involves a 2005 land deal first reported by the Chicago Tribune. Obama and the wife of Tony Rezko, a politically connected Chicago developer who's since been indicted in connection with paying kickbacks, bought adjacent plots of land on the same day. Months later, Obama bought back part of the Rezko parcel to expand his $1.65 million home's lot.

The revelation stunned government watchdogs, because in the Illinois Senate and on Capitol Hill, Obama flaunted his reputation as a clean-government champion. He has urged tighter fundraising and disclosure rules and railed against getting too cozy with lobbyists.

Obama, who'd known Rezko since the early 1990s, later said it was "boneheaded" of him not to anticipate how the sale would look; he returned Rezko's contributions.

Critics have found no evidence that he did legislative favors for Rezko.

But Cindi Canary, the executive director of the Illinois Campaign for Political Reform, said the deal still gives her pause.

"More than anything else, there was a sense that Sen. Obama should have known better," she said. "One is judged by the company one keeps. Tony Rezko was a very well-known wheeler and dealer in Illinois politics, someone who for a number of years had a swirl of trouble around him and allegations before the final indictment came down."

Rival Democrats have painted him as too green on foreign policy to serve as a wartime president.

Sen. Hillary Clinton, D-N.Y., called Obama "irresponsible" and "naive" when he said he'd be willing to meet with the leaders of nations that the United States considers hostile, such as Iran and North Korea.

Sen. Joseph Biden, D-Del., criticized Obama for a speech in which he said he'd invade U.S. ally Pakistan if necessary to get high-level terrorists. Biden's issue wasn't Obama's willingness to invade so much as his broadcasting it. That, Biden said, could undermine Pakistan's president and damage U.S. interests.

Obama raises the experience question in his own campaign speeches, painting his rivals as cynics and arguing that his mix of youth, background diversity and civic engagement would better serve the nation.

Voters often ask Obama which president he admires most. He usually says Abraham Lincoln, who ended slavery, managed the country through civil war — and delivered one of history's most famous speeches, the Gettysburg Address.

But Obama sometimes betrays a yearning to be viewed like John F. Kennedy, to set a style of leadership that reinvigorates public faith in government.

"One of my jobs as president is to make government cool again," Obama told an engaged college crowd in New Hampshire this fall.

Because of Kennedy, Obama said, "thousands of young people were inspired to say, 'I want to give something back; I want to serve.' Now we're losing that. And we've got to restore it."