Former U.S. president Bill Clinton takes to the stage at the 2012 Democratic National Convention tonight with a clear mission.

He must build on the energy generated during the convention's first day, particularly the speech by Michelle Obama, while laying out why President Barack Obama's vision of rebuilding the American economy is a reflection of the policies that led to a huge budget surplus during Clinton's eight years in office.

As it turns out, no Democrat may be in a better position to boost Obama's fortunes: A USA Today/Gallup poll conducted prior to both political party conventions suggests Clinton has a 69 per cent favourable rating — a personal best spanning his presidential and post-presidential years. Among women, his rating is 73 per cent.

"I think that better than anyone he can make the case for President Obama," James Carville, Democratic strategist and manager of Clinton's 1992 campaign, told CBC News at the convention centre in Charlotte, N.C.

Clinton's appearance is considered so crucial that Vice-President Joe Biden was bumped out of the precious Wednesday night spot, and will be barely a footnote on Thursday when he introduces Obama.

"He is a [rock star]. Clinton still remains extremely popular with the American people, let alone with Democrats," said Ronald Hattis, a California delegate. "His wife was the main rival of Barack Obama and showing unity between the Clintons and the Obamas is a keystone to holding everybody together."

Clinton's speech comes at a time when unemployment is at 8.5 per cent and the economy remains fragile. The hope is that Clinton can remind voters that it was his presidency, a Democratic presidency, where the budget was in surplus and the economy robust.

Clinton speech 'very significant'

Enlisting such a popular former president, also known for his gift of oratory, might seem slightly risky, by allowing Clinton to snatch some of the spotlight.

"Obama asking president Clinton to make this speech is very, very significant because it shows Obama's not afraid of showing someone who's probably one of the great keynote speakers of all time," Lanny Davis, who served as Clinton's special counsel, told CBC News.

Former U.S. president Bill Clinton also spoke during the Democrats national convention in 2008. (John Kolesidis/Reuters)

Clinton, he believes, will talk about the policies he most supports, such as health care, stress what a difficult economic hand Obama was dealt and that Obama's policies are far superior going forward to those Republican presidential candidate Mitt Romney is proposing.

Clinton, no doubt, will triumph his own economic record during his presidency, but Davis has no worries that voters may unfavourably compare Obama's economy.

"Bill Clinton didn't inherit the greatest recession since the Great Depression, the most disastrous plummeting of the economy," Davis said. "Everybody knows how bad we were in 2009. They can't compare to 1993 when Bill Clinton became president."

The former president spoke on behalf of Obama at the 2008 convention in Denver. But that was more about healing, following a bitter primary battle between Hillary Clinton and Obama, Davis said.

“Last time, it was necessary because of the anger and the bitterness between the Obama camps and the Clinton camps. Helped ease the pain, so to speak. Now it's about re-election," Davis said.

That campaign soured the relationship between Clinton and Obama. Clinton felt that Obama was rejecting his place in presidential history. And Clinton fumed when the Obama campaign accused him of veiled racism when he compared Obama’s primary victory in South Carolina to Jesse Jackson's win in that state.

"I'm still angry what they called Bill Clinton, what they did to Bill Clinton. It was mean. I'm sure President Clinton doesn't forget that," Davis said.

Frosty relationship thawing

But Clinton, for his part, has annoyed the Obama administration for some of his off-the-cuff remarks. In one interview, Clinton said he supported extending the Bush income tax cuts. In another, he said , in reference to Romney, that "a man who has been governor and had a sterling business career crosses the qualification threshold."

He also suggested the Democrats should scale back on their attacks on Bain Capital, the private equity firm founded by Romney. New York’s attorney general is investigating tax strategies of some of the country's largest private equity firms, including Bain Capital.

Yet some say the once frosty relationship has begun to thaw, in part, because of Hillary Clinton’s role in the Obama administration. “I would say it’s warming very well,” Carville said.

Clinton could go off message However, a recent article in The New Yorker could cool things off again. It stated that according to unnamed sources, in 2008, Clinton told Ted Kennedy, in reference to Obama: ‘A few years ago, this guy would have been carrying our bags."

However, Davis slammed the accuracy of the article.

"It's absolutely ludicrous to rely on somebody who passed away who told somebody who told somebody, and it's published…in The New Yorker," Davis said. "It's impossible Bill Clinton uttered those words to Ted Kennedy."

Wednesday night's speech runs the risk of having Clinton go off message. There have been questions over how much of his speech has been or will have been vetted by convention officials before he makes his appearance.

"Bill Clinton is not bound by anybody, and he could go off message and he has occasionally disagreed with Obama, so there's a little bit of tension and suspense of what he's actually going to say,” said Hattis. "But he's very smart. He doesn't want to blow the election, so I'm sure it will be supportive."

Davis said he's sure Clinton has done some checking with the Obama campaign and they've looked over what he's written.

"But knowing Bill Clinton — a minute before the state of the union speech, he was scribbling his own [words].

"One thing I know is he's dedicated to strongly supporting Obama because of his policies. He does not agree with Mitt Romney's policies. He does not agree with Mitt Romney's ideas. And that's what drives Bill Clinton, ideas more than personality."

On Tuesday night, Michelle Obama capped a night of speeches aimed at the Democratic core with a speech widely viewed as a major boost for her husband.

Explaining why her husband has the moral fortitude to take on the challenges of the U.S. presidency, she said:

"After so many struggles and triumphs, and moments that have tested my husband in ways I never could have imagined, I have seen first-hand that being president doesn’t change who you are," Michelle Obama said, to a crowd chanting "four more years" in the Time Warner Cable Arena. "It reveals who you are."

Just before she spoke, the mayor of San Antonio, Texas, Julian Castro, the keynote speaker of the night and rising political star of the Democratic Party, had given his own endorsement of the president.

"Our choice is a man who has chosen us," Castro said.

Newark Mayor Cory Booker got the enthusiastic crowd on its feet early in the convention, and they mostly maintained a high level of energy, responding loudly and boisterously to a number of speakers, including Castro, Massachusetts Gov. Deval Patrick and former governor of Ohio Ted Strickland.