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 Wisconsin.  “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.  And an Arizona woman, Stacey Lihn, took the stage with her toddler, Zoe, who has a congenital heart disease, and said her daughter’s health insurance would run out if Mr. Romney won and followed through with his promise to get Mr. Obama’s health care law repealed. “But we’re also scared,” she said. “Governor Romney repealing health care reform is something we worry about literally every day.”  The Democrats even got the spirit of Senator Edward M. Kennedy of Massachusetts into the act in a tribute video. It showed Mr. Kennedy in his 1994 debate with Mr. Romney during their Senate race, mocking Mr. Romney for his shifting position on abortion rights and calling him “multiple choice.”  The program never addressed the disappointment of many wavering Obama voters in the president’s handling of the economy, as Republicans will note. But the speakers pounded Mr. Romney on immigration, on health care, on Medicare, on foreign policy, on the 2009 auto bailout and on his tax policies, which they said would benefit the rich at the expense of the working class and cause the kind of economic damage that they said Mr. Obama had worked to undo.  Mr. Romney’s wealth was given full attention, with Gov. Martin O’Malley of Maryland referring to the Swiss bank account Mr. Romney no longer has by saying: “Swiss bank accounts don’t put cops on the beat or teachers in our classrooms. Swiss bank accounts never created American jobs.”  Apparently concerned about alienating voters with too much negativity, Mr. Obama’s strategists were careful to ensure that speakers always included a positive element about Mr. Obama.  “Mitt Romney is walking away from us,” Representative Nydia M. Velázquez of New York said. “He walks with people who disrespect us and people who divide us and people who do not believe that the American dream means all of us. President Obama has walked with us for the last 12 years — in good times and in tough times — and right now we are going to walk with the president to the polls and onward to victory.”  Mindful of the need to address a sometimes deflated group of liberal, grass-roots supporters, speakers stressed core party social issues like abortion rights and the president’s support for gay marriage.  A group of Democratic women in the House of Representatives came to the stage together — led by Representative Nancy Pelosi of California, the minority leader — to criticize Republican moves against the so-called Lilly Ledbetter Fair Pay Act, which would make it easier for women to press discrimination cases, and various elements of the president’s health care overhaul, including its coverage of contraception.  When Mayor Cory A. Booker of Newark gave a speech introducing the party platform and its first-ever declaration of support for same-sex marriage,” the delegates broke into a standing ovation and cheers of “Cory!” and “U.S.A.!”  “No matter who you are, no matter what color or creed, no matter how you choose to pray or who you choose to love,” Mr. Booker shouted, “if you are a citizen of the United States of America, you should be able to find a job that pays, you should be able to afford health care for your family, you should be able to retire with dignity and respect, and you should be able to give your children the kind of education that allows them to dream even bigger, to go ever farther and accomplish more than you could ever imagine.”  A version of this article appears in print on September 5, 2012, on page A1 of the New York edition with the headline: First Lady Tops Opening Night For Democrats. Order Reprints| Today's Paper|Subscribe
Democrats had two simple messages for voters: Mitt Romney does not get it, and President Obama does. The main attraction was Mr. Obama’s lead character witness: his wife, Michelle.