Barack Obama will have to draw on all his considerable oratorical skills tonight to connect himself to those parts of the electorate that remain unconvinced by his message and unclear about what he represents.

"He will be addressing the single largest audience he will have at any time between now and the election, so it's important to use the event to make clear where he stands on matters that are worrying voters," said Ted Sorensen, John F Kennedy's chief speechwriter.

"Obama is the first presidential candidate who reminds me of Kennedy's eloquence and capacity to inspire. They both, despite their own special backgrounds, convey to people that they understand and listen to every American citizen."

To a large degree, the success of Obama's presidential run so far has been built on his skills as a speechmaker. It was his speech to the Democratic convention four years ago, before he had even entered the Senate, that propelled him into the national spotlight.

"He is blessed with a richly resonant voice that we love to hear; he could read the telephone directory and it would sound good," said Ted Widmer, editor of an acclaimed edition of American political speeches and a former Bill Clinton speechwriter. "He is very good at pauses and inflection, and he cuts an impressive figure on stage - all of which adds up to making an Obama speech a special event."

The Kennedy link is evident within Obama's own team of speechwriters. Adam Frankel, a graduate of the London School of Economics, spent six years working with Sorensen on his memoirs - immersing himself in the process in Kennedy's oratory. Frankel is 26, as is Obama's chief speechwriter, Jon Favreau, or Favs as he is known, who used to work for John Kerry.

A third important scribe recently joined the Obama campaign. Sarah Hurwitz was Hillary Clinton's main speechwriter during the primary season, a role she previously performed for General Wesley Clark in his 2004 bid.

Obama is clearly surrounded by youthful talent, though what is less clear is how much he depends on it. He has told reporters that he personally began writing tonight's address while on holiday this month in Hawaii.

But demonstrating his now well-proven ability to inspire a crowd will be only part of the challenge for Obama tonight. Crucially, he must also tiptoe his way through the sensitive issue of race. The question of how much reference he makes to his potential to make history as America's first black president is all the more loaded because today is the 45th anniversary of Martin Luther King's famous "I have a dream" speech in front of the Lincoln Memorial.

"It's a complicated calculation," said Randall Kennedy, a professor at Harvard law school. "On the one hand, he can't go wrong in invoking such an iconic speech that has become part of Americana. On the other hand, the more Obama talks about race the blacker he becomes - and America still has a massive race problem."