SPRINGFIELD, United States (AFP) - Senator Barack Obama (news, bio, voting record) launched “an improbable quest” to become America’s first black president, audaciously invoking Abraham Lincoln, the US president who ended slavery.

“I want us to take up the unfinished business of perfecting our union, and building a better America,” Obama told a crowd of thousands in temperatures of minus 11 degrees Celsius (13 Fahrenheit) in Lincoln’s hometown.

“You didn’t come here just for me, you came here because you believe in what this country can be,” said the Illinois senator, 45, muscling his way into a packed Democratic field already dominated by New York Senator Hillary Clinton.

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