The last night of the Democratic National Convention was switched from outdoors at the 74,000-seat Bank of America Stadium to inside the Time Warner Stadium, which holds 50,000 fewer, because of a theatening weather forecast.
MSN.com predicted isolated thunderstorms in the Charlotte area Thursday night.
"I know it's disappointing," Obama told volunteers by conference call. " ... And I know it's especially disappointing for a lot of you who worked hard to get your tickets to the event, or traveled or planned to travel a long way at your own expense to be here.
"So all I can tell you is how much I appreciate everything that you've done," he added. "Some of you earned your tickets through the 9-3-1 program -- nine hours of volunteer work over three days for a community credential ticket."
He thanked them for their enthusiasm, but said, "My main message is we can't let a little thunder and lightning get us down. We're going to have to roll with it. And while we may not be able to be together in person, I hope you're still going to gather together at community watch parties that are happening not just here in Charlotte, but all across North Carolina, all across the rest of the country. I hope you tune in tonight, watch the speech together. Let me know what you think afterwards."
Obama should be allowed to finish the job he started, former President Bill Clinton said Wednesday as Obama prepared to deliver his party's acceptance speech Thursday.
"President Obama started with a much weaker economy than I did," Clinton told the Democratic National Convention in Charlotte, N.C. "No president -- not me, not any of my predecessors -- could have fully repaired all the damage that he found in just four years.
"But he has laid the foundation for a new, modern, successful economy of shared prosperity," Clinton said in a 45-minute prime-time, nationally televised address.
Clinton said the Republican ticket of Mitt Romney and Paul Ryan represents "a winner-take-all, you're-on-your-own society," while the ticket of Obama and Vice President Joe Biden would bring "a country of shared opportunities and shared responsibility, a we're-all-in-this-together society."
"We simply cannot afford to give the reins of government to someone who will double down on trickle down," Clinton said, adding, "I love our country so much and I know we're coming back."
He said: "Is the president satisfied? Of course not. But are we better off than we were when he took office? The answer is yes."
Clinton spoke on the day Obama arrived in Charlotte. Obama made a brief appearance at the convention, hugging Clinton on the stage after his impassioned plea on behalf of Obama's re-election and nominating him for a second term.
Convention delegates conducted the ceremonial roll call vote after Clinton's speech, with Ohio putting Obama over the top and formally elevating him as the party's presidential nominee at 12:06 a.m. EDT.
Obama was to deliver his acceptance speech Thursday night.
Threats of severe weather forced convention organizers to move the speech, scheduled to begin at 10:10 p.m. EDT, indoors at the 20,200-seat Time Warner Cable Arena, where the convention is being held. AccuWeather and other forecasters predicted thunderstorms in Charlotte during the 10 p.m. hour.
Convention organizers had planned to stage the speech to a crowd of at least 65,000 supporters at the open-air Bank of America stadium in a reprise of Obama's 2008 acceptance speech in Denver, when he delivered an outdoor acceptance speech at Mile High stadium before some 84,000 people.
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