Obama wowed the crowd, estimated at 6,000, at Iowa State University in Ames before heading to Fort Collins, Colo., and an appearance at Colorado State University.
En route to Ames, Obama campaign spokeswoman Jen Psaki told reporters the president was paying attention to developments in the Gulf of Mexico and would alter his campaign swing should Hurricane Isaac devastate the gulf coast.
As he began speaking, Obama said officials have been readying for the storm for days.
"America will be there to help folks recover, no matter what this storm brings because when disaster strikes, we're not Democrats or Republicans first. We are Americans first," Obama said to applause.
"We're one family. We're one family and we help our neighbors in need."
Obama, whose 2008 campaign galvanized young voters, attempted to recreate the magic.
"Your vote decides where we go from here," he said, returning to familiar campaign themes, pointing out policy differences between him and Mitt Romney, who is set to become the GOP presidential nominee this week.
"Last week my opponent's campaign went so far as to write you off as a lost generation. That's -- that's you, according to them," he said.
"They -- and then what they hope is that by telling you these things you'll get discouraged and you'll just stay home this time. But -- but -- but you can't -- you can't believe it. The -- I don't believe it."
Speaking later to students at Colorado State University in Fort Collins, Obama said of Republicans: "On issue after issue, these guys seem to just want to go backwards. Sometimes they want to go back 10 years, sometimes 20, sometimes 50, sometimes 100. This isn't the time to refight battles that we've already settled. In November you can say that in this century, women should be trusted to make their own healthcare decisions. ... That's not who we are. We go forward. We don't go backwards."
Democratic Party leaders say the party plans to let loose a flow of criticism directed at Romney this week in hopes of disrupting the Republican National Convention message, The New York Times reported.
The Democratic National Committee said its plans call for linking Romney to comments on rape by Todd Akins, a Republican congressman running for the Senate in Missouri, and an Obama-supporting super PAC will unveil a television ad attacking the impact of Romney's policies on the middle class.
Republicans planned to show a video Tuesday at the convention featuring voters who backed Obama in 2008 but now say they will vote for Romney in November.
Obama and Democrats must walk a fine line between aggressive campaigning and sensitivity as Hurricane Isaac barrels toward Gulf Coast states and New Orleans, observers told the Times. Wednesday is the seventh anniversary of the day Hurricane Katrina made landfall in 2005.
It's a matter of timing and intensity, observers say. If Obama goes to the gulf coast this week -- and rains on Romney's acceptance of the GOP nomination -- critics could say the president was putting politics ahead of his presidential duties. If he waits until after the RNC runs its course, Obama still could be accused of putting politics ahead of his presidential duties.
Observers said Obama and Democrats must decide how hard to campaign and attack their opponents, and whether Obama should cut short his campaign swing or still rally supporters as Isaac pounds ahead.