The US Democratic Party has opened its nominating convention to launch President Barack Obama\'s campaign for a second term in the November elections. First Lady Michelle Obama is the top speaker on the opening night of the convention in Charlotte, North Carolina, where 6000 delegates are attending the centre-left party\'s three-day gathering. \"I know that whatever I say here today, it\'s going to be at best a distant second to the speech you will hear tonight from the star of the Obama family, Michelle Obama,\" the president told a rally on Tuesday in Norfolk, Virginia. \"I\'m going to be at home, and I\'m going to be watching it with our girls,\" Obama said of his wife\'s speech. \"And I am going to try not to let them see their daddy cry.\" With unemployment stuck above 8 per cent and second-quarter growth at an annual rate of 1.7 per cent, Democrats were labouring this week in Charlotte to rediscover the same enthusiasm that swept Obama to power four years ago. Obama will arrive on Wednesday in Charlotte and will give his acceptance speech on Thursday to an estimated 70,000 people in a football stadium. The conservative Republicans last week formally named Mitt Romney their candidate to challenge Barack Obama. As first lady, Michelle Obama has emphasised social causes and healthy living, promoting exercise and healthier diets particularly for children, in response to rising US obesity rates. Anne Kilpatrick, a delegate from South Carolina, hailed Michelle Obama\'s \"example of healthy living\" including by planting a vegetable garden on the White House grounds. She called the first lady \"the single most inspiring person in Barack Obama\'s life, as far as I\'m concerned\". \"They\'re a team and always have been,\" Kilpatrick said. Democratic campaign spokeswoman Jen Psaki said Michelle Obama would give \"a personal and passionate speech\" about what drives her husband and his values. Romney\'s wife, Ann, gave a similar address in a bid to show the personal side of her husband last week. Tuesday\'s speakers include San Antonio Mayor Julian Castro, the first Hispanic person to give a keynote address at the party convention. The key speaking slot pegs him as a rising star within the party, which is eager to reinforce its appeal to the growing Latino population in the United States. The Republicans have focused on the lagging economy and persistent high unemployment to tell convince voters to make a change. \"Are you better off now than you were four years ago?\" vice presidential candidate Paul Ryan asked at a rally on Tuesday. Obama has attacked his opponents\' policies as regressive. \"On issue after issue, Governor Romney and congressman Ryan want to take us backward,\" he said in Norfolk. \"But the story of America is not about going backward. It\'s about going forward.\"