***UPDATE*** The Washington Post reports that Obama will use the speech to outline a new direction for America:
A day after Democrats officially named him as their presidential candidate, Barack Obama goes before a stadium crowd Thursday night to formally accept the nomination and lay out a plan to lead the nation in a new direction at home and abroad...
...In the speech, which caps the four-day Democratic National Convention and opens Obama's campaign for the White House as his party's nominee, Obama will offer "a fundamentally new direction to get America back on track, both here and around the world," said David Plouffe, his campaign manager. Appearing on morning television talk shows, Plouffe said Obama would explain his plans for dealing with the economy, health care and education, as well as international challenges such as threats to the United States and strained relations with other countries.
***UPDATE*** ABC News lists what they think Obama needs to accomplish with his speech tonight:
Barack Obama's chief challenges tonight are to persuade voters he's sufficiently seasoned for the presidency, better define his theme of "change" and cement his advantages on key domestic issues, chiefly the economy.
There's more: Obama needs also to expand his support among older, more reliable voters; maintain his lead on personal attributes such as empathy; protect himself on consistency; and capitalize on his advantages in enthusiasm and an aura of optimism.
And, as much as any other, to tie John McCain to the unpopular George W. Bush.
Not a short order for a night's work, but potentially a crucial one. The contest has been close; 49-45 percent Obama-McCain among likely voters in our pre-convention poll. Arguably that's closer than it should be, given the flight from the Republican Party and the broad public discontent that's accompanied the faltering economy, the unpopular war in Iraq and dissatisfaction with the incumbent president.
Barack Obama gave the Wall Street Journal a little preview of his Thursday night speech:
Barack Obama said he plans to focus on the struggles of middle-class Americans, including their tax burden, in his Thursday night speech accepting the Democratic nomination for president.
"The single most important thing I have to make clear is the choice we have in November between the same failed policy of the last eight years for the middle class and the new agenda to boost income for Americans and help families who are struggling," he said in a brief interview with The Wall Street Journal Tuesday. "I will make that contrast very clearly."
ABC News has more on Obama's speech-writing process:
Because of the protracted primary season, Obama is playing catch-up a bit. He wrote an outline while on vacation in Hawaii, but didn't get any time for serious work while there with his family.
To prepare, he read the convention acceptance speeches of former Presidents Franklin Roosevelt, Harry Truman, John F. Kennedy, Ronald Reagan, George H. W. Bush, and Bill Clinton, as well as less successful Democratic presidential nominees Vice President Al Gore and Sen. John Kerry, D-Mass.
In addition to laying out his plans and providing some inspiring oratory -- though not as much as in 2004, aides cautioned -- one of the goals of the speech is to argue that Sen. John McCain, R-Ariz., is no maverick, but rather, someone who represents a doubling-down of the current policies of President George W. Bush.
Meanwhile, John McCain staffers are already mocking the stage on which Obama will appear. Reuters reports that it will look like "a miniature Greek temple." ThinkProgress points out that the Virginia Republican Party went for a similar style at their convention this year.
For more Huffington Post coverage from the Democratic National Convention, visit our Politics @ the DNC page, our Democratic Convention Big News Page, and our HuffPost bloggers' Twitter feed, live from Denver.
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