"You have done so much so far," Plouffe told the crowd at Invesco Field at Mile High Thursday during the final session of the Democratic National Convention in Denver. "I'm asking (you) ... to dedicate a few hours this weekend in a massive voter registration drive, the likes of which have never been seen."

The convention moved to the stadium, Plouffe said, to open the proceedings up "to all America" as the Illinois senator accepts the Democratic nomination to become the first black major-party presidential candidate.

In Pennsylvania alone, Plouffe said, volunteers already registered 316,000 new Democratic voters, and campaign officials believe another 100,000 can be registered before Election Day, Nov. 4.

"This election will be here before we know it," Plouffe said. "There is no time to lose."