"You can't sit it out," he said during the call. "You can't suddenly just check in once every 10 years or so -- on an exciting presidential election -- and then not pay attention during big midterm elections, where we've got a real big choice between Democrats and Republicans."
Two years ago, young voters turned out in droves, voting overwhelmingly for Obama.
In the most recent ABC News/Washington Post poll, 55 percent of voters 18-29 said they were "absolutely certain" to vote this fall. That's compared to 78 percent among 50- to 64-year-olds and 77 percent of those 65 and older.
A recent poll by Rock the Vote showed that 60 percent of young Republicans were very likely to vote, compared to 51 percent of young Democrats. And today at a fundraiser in New Hampshire, Vice President Joe Biden urged Democrats to "remind our base constituency to stop whining and get out there and look at the alternatives."
At a February 2008 rally for Obama, there may have been no one more spellbound than University of Wisconsin student Bryon Eagon.
"We have given young people a reason to believe and we have brought the young at hearts back to the polls who want to believe again," Obama said during the event.
He then acknowledged Eagon. "I want to thank also my director of Wisconsin Students for Obama, Bryon Eagon, who has been working like a madman to help get this organized here tonight. Thank you."
Eagon says today that excitement and engagement is not close to what it was two years ago.
"It's going to be a challenge but it's a challenge worth waging," he said. "We're hopeful that once students learn about the election, who is on the ballot and what issues are at stake that we will once again show up to vote and vote for Democrats."
Polls today show diminished enthusiasm among young voters nationally -- bad news for Democrats because young voters tend to lean left.
"They're paying attention. They want to participate," said Heather Smith, executive director of Rock the Vote.
"But they're starting to increase in their cynicism about the political process."