WASHINGTON - (AP) -- Twelve years ago to the day, an obscure Senate candidate from Illinois catapulted himself to the center of American political consciousness with a rousing convention speech in Boston. Barack Obama returns to the convention stage Wednesday as the battle-hardened president hoping his legacy won't be eroded by the outcome of the election to replace him.

It's hard to overstate what Obama has at stake as he implores voters to elect Hillary Clinton during his speech to the Democratic National Convention in Philadelphia. Take Republican Donald Trump at his word, and if elected, he'd undo just about everything Obama has done, from climate change and immigration to trade and foreign relations.

So after his wife, Michelle Obama, brought delegates to their feet with a stirring speech Monday evening, Obama stayed up late into the night fine-tuning his words, the White House said. His speech will combine an affirmation of Clinton's judgment and fortitude with a rebuke of the scare tactics he accuses Trump of deploying.

"The president will talk about who we are as a country and that we are better united than divided, and that we're better together than apart," said White House spokesman Eric Schultz.

That Democrats are so eager for Obama to grace the convention stage is a reflection of how dramatically things have changed from just two years ago, when Democrats practically begged an unpopular Obama to keep his distance from the campaign trail. His approval ratings have since recovered, though a solid majority of Americans still feel the country is moving in the wrong direction.

His vice president, Joe Biden, also will address the convention on Wednesday, in a reminder to some Democrats that the candidate they wanted this year was the one they couldn't have.

With his last State of the Union address behind him, Obama's speech in Philadelphia will be one of his final opportunities to define and defend his tenure with a massive audience watching. Tens of millions have been tuning in to the conventions in primetime this year.

Democrats are hoping that Obama is uniquely positioned to persuade wary voters that Clinton is right for the job and to vouch for the trustworthiness of a nominee most voters say they still don't trust. White House officials have described him as a "convert" to Clinton's cause who, after fighting her bitterly in the 2008 Democratic primary, saw her abilities firsthand when he named her secretary of state.

If there's a sense of history coming full circle, it may be in the historic nature of Clinton's candidacy. The first African American president will deliver his speech the day after the first woman was nominated by a major political party.

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