CHARLOTTE, N.C. — Democrats opened their convention here on Tuesday night with a parade of officials telling voters that Mitt Romney does not get it and with a rousing speech from Michelle Obama making the case that President Obama does.


Mr. Obama’s roster of Democratic promoters spent the first hours detailing a political indictment of Mr. Romney, blistering him as being out of touch with the middle class and intent on taking the country back to the policies that caused the economy’s problems.


But the main attraction of the evening was the appearance of Mr. Obama’s lead character witness: the first lady, who, wearing a pink-and-gold-speckled sleeveless dress, was greeted with chants of “Four more years!” from the excited arena, to which she responded: “With your help.”


“Barack knows what it means when a family struggles,” she said in remarks that electrified the party faithful in the Time Warner Cable Arena and were broadcast nationally by the television networks. “He knows what it means to want something more for your kids and grandkids. Barack knows the American dream because he’s lived it, and he wants everyone in this country to have that same opportunity, no matter who we are, or where we’re from, or what we look like, or who we love.”


Four years of partisan sniping, Washington gridlock and continued economic challenges may have dulled the luster of the man this party nominated four years ago. But Mrs. Obama sought to remind his 2008 voters that the same person they supported then is underneath the tarnish she sought to buff away.


The address was meant to lay the foundation for a convention program devised to remind wavering working- and middle-class voters — the same ones Mr. Romney is working so hard to woo away — what they liked about the president when they supported him four years ago, and how his own humbler roots have helped inspire his policies to help them.


“He believes that when you’ve worked hard, and done well, and walked through that doorway of opportunity, you do not slam it shut behind you,” Mrs. Obama said, her impassioned delivery drawing the crowd to its feet as it waved red, white and blue “Michelle” placards. “You reach back, and you give other folks the same chances that helped you succeed.”


It was one of the few times Mrs. Obama came close to even a subtle reference to the very direct argument being made against her husband’s opponent here. She argued that Mr. Obama’s experience as president had taught him that “no amount of data or numbers will get you the right answer.” Her portrait of her husband was the inverse of the one that other Democrats have sketched of Mr. Romney, who former Gov. Ted Strickland of Ohio said viewed the “American worker” as “just numbers on a spreadsheet.”


As someone with whom she was “so young, so in love, and so in debt,” Mrs. Obama said, her husband believes “success isn’t about how much money you make. It’s about the difference you make in people’s lives.” 


Mrs. Obama’s was almost the only voice lacking an explicit anti-Romney edge, conveying a personal tone and touch after speeches that were personal in a different way when it came to the president’s opponent. As the other speakers undertook a program that amounted to a thundering response to the Republican convention last week in Tampa, Fla., they went after Mr. Romney on just about every conceivable issue.


The keynote speaker, Mayor Julián Castro of San Antonio, offered the overarching argument against Mr. Romney and his running mate, Representative Paul D. Ryan of Wisconson.


“Their theory has been tested. It failed. Our economy failed,” Mr. Castro said in what seemed to be the second-most rousing speech of the night for the Democratic audience. “The middle class paid the price. Your family paid the price. Mitt Romney just doesn’t get it.”


After what has at times been a tentative approach to promoting the health care law, perhaps Mr. Obama’s signature legislation, the program included a full-throated defense of the overhaul and the Supreme Court’s decision to uphold it.