It came after a partial roll-call vote that was ended by former rival Hillary Clinton. She asked convention delegates to declare Obama the nominee by acclamation. Clinton made her motion to suspend the roll-call vote "in the spirit of unity, with the goal of victory."
Chants of "Obama" and "Yes we can" floated up from the convention floor as Obama's victory was sealed.
Obama was in Denver at the time, but not at the convention. His aides say it's possible he could make a brief visit at the Pepsi Center to thank his suppoters.
His formal acceptance will be tomorrow night at a nearby football stadium. Some 75,000 people could attend.
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