IOWA CITY, Iowa — US President Barack Obama is giving his newly crowned Republican foe Mitt Romney a taste of the fight to come, assembling capacity crowds of fired-up young voters in a blitz of swing states.

Obama dropped into university campuses in North Carolina, Colorado and Iowa, drumming up throngs of 8,000, 11,000 and 4,100 respectively over the last two days in an test of the organizing power of his new political machine.

But though the president, who joked his way through a skit on a late-night talk show Tuesday, clearly wins the "cool" vote over the starchy Romney, he cannot take the enthusiasm of young voters for granted.

In 2008, in his victory over the Republican candidate, Senator John McCain, Obama attracted 66 percent of voters aged between 18 and 26.

A recent Wall Street Journal/NBC News poll suggested that Obama enjoyed a similar edge over Romney just over six months before the general election, leading among 18 to 34-year-olds by 60 percent to 34 percent.

At the equivalent moment in 2008, 63 percent of the group expressed high interest in the election. But now, just 45 percent are showing an interest, potentially putting the Obama advantage into question.

"Last time, I had more excitement mainly because it was the first time I was voting. But his campaign seemed more hopeful," said Matthew Goo, 22, who lined up to see Obama at Colorado University.

Goo put his finger on the key question for the Obama campaign. Will the students and young voters seduced by an inspirational once-in-a-lifetime campaign in 2008 judge that Obama failed to live up to the hype?

"It will be difficult to reproduce in 2012 the sense of excitement that led to the surge of young voters in 2008," said Brookings Institution scholar Thomas Mann.

"The poetry of the 2008 campaign gave way to the prose of governing. Tough economic times and constraints on presidential leadership have taken their toll."

Obama hopes to repeat his 2008 victories in North Carolina, Iowa and Colorado en route to a second White House term on November 6, and the strength of the youth vote could be important in close contests.

Four years ago, for instance, the Democratic president captured North Carolina, a traditional southern conservative state, by less than one percent -- and he scored well in college towns.

Obama anchored his two-day tour on a bid to convince Congress to stop the interest rate on student loans doubling from the current 3.4 percent.

A large part of a candidate's task in every election is to show voters he cares about them and identifies with their struggles.

Obama went out of his way on his two-day tour to show he gets the pain inflicted by the huge cost of college education in the United States, which can run to tens of thousands of dollars a year, saying it wasn't long ago he was in the same boat.

"This is personal. We have been in your shoes. we didn't come from wealthy families," Obama said, of he and his wife Michelle, noting that when he grew up his father "wasn't around" and he was brought up by a single mother.

"I am President of the United States (but) it was only about eight years ago that we finished off paying off our student loans," the Harvard law graduate said as students laughed in a gym at the University of Iowa on Wednesday.

Obama's empathy also appears to be designed to draw a sharp contrast with his multi-millionaire, former venture capitalist foe Romney.

But Romney, the former Massachusetts governor, who on Tuesday effectively wrapped up the Republican nomination to take on Obama in November, has signaled a fight is on for the youth vote.

"Young voters should see this tour for what it really is: an election-year gimmick that will do nothing to bring much-needed jobs to our nation's young adults and recent graduates," Iowa Governor Terry Branstad said Wednesday.

Branstad, a Romney supporter, pressed home the campaign's attack that a vote for Obama was a vote for economic uncertainty and diminished prospects.

"Young voters across the country will face a clear choice this fall: they can choose President Obama -- and his record of fewer jobs and higher debt.

"Or they can choose Mitt Romney, who will lead us to greater prosperity and a bright future."

Obama met that attack here on Wednesday, seizing on a claim by a Republican aide that he was only focusing on student loans to distract attention from the uncertain economy.

"These guys don't get it. This is the economy. This is about your job security, this is about your future. You are the economy," Obama told the students.