Younger voters were the foot soldiers for Barack Obama in 2008. Now, the president's campaign team says they will be his secret weapon for 2012. 

But while 18-to-29 year-old Americans are reliable Democrats, their enthusiasm for Obama and presidential politics has waned, setting the stage for an uphill struggle to turn out the vote.

Forty-nine percent of millennial voters approve of Obama, according to the Pew Research Center, down 23 points from February 2009.  They are also the least interested in or engaged with the current campaign, the study found. 

Only 17 percent of millennials said they are following election news closely, while just 13 percent said they've given a lot of thought to the candidates, a 15 point drop from the same period four years ago.

"They're still very supportive of the president in the head to head match-up in a test race with Mitt Romney," said Pew researcher Carroll Dougherty. "Very supportive, almost supportive as they were of Obama in 2008."

"But this enthusiasm gap has got to be worrisome for Democrats because this was Obama's strongest age group in 2008," he said. "It looks to be his strongest age group still, but the question is how many actually turn out."

Making the dynamic even more challenging for Obama is the perception among millennials that Obama will lose his bid for a second term.  Thirty-six percent in a poll this month by the Harvard University Institute of Politics said the president would lose while just 30 percent said they thought he'd win.

"I would honestly have to say I'm not as enthusiastic as before," said Girish Balakrishnan, 21, of New Jersey, who cast his first vote for Obama in 2008.

"The last time there was a lot more pressure and times were tougher at the time and there was a lot more need for change," he said. "I really haven't seen much out there in terms of a convincing argument and such."

The Obama campaign has made outreach to younger voters on college campuses a top priority and plans to continue a concerted effort to enlist new volunteers and register first-time voters in the early months of 2012.

"There's 8 million registered voters who are 18 to 21 who weren't old enough to vote last time, who are going to cast their first vote for Barack Obama," said a confident Obama campaign manager Jim Messina at a youth rally on the University of Pennsylvania campus earlier this year. Messina says young voters could make the difference in key swing states like Pennsylvania, North Carolina and Virginia.

An outreach initiative dubbed "Greater Together" relies heavily on social media and grassroots organizers to emphasize what aides say are Obama's youth-friendly accomplishments, like ending the war in Iraq, repealing "don't ask don't tell" and health insurance reforms that allow younger Americans to remain on their parent's health plans.

But recent interviews with a number of college students across the country indicate the Obama campaign's message has yet to take hold.

"I would give him a 'B,' I guess," said Caroline Nelson, a 27-year-old medical student from Chicago, when asked to rate Obama's record. "I think that he compromised a couple of the issues I thought he was really going to push for, especially the environment which is an important one to me. … My early thought is that I would probably still support him but I'd like to see him take a stronger campaign."

James Malazita, 25, a communications major at the University of Pennsylvania, said he "got pretty much what I expected out of Obama."

"I always feel like Obama's portrayed pretty left when he's actually pretty centrist," he said. "I haven't seen any better options yet."

Perhaps more of a challenge for Obama than reengaging past supporters will be winning over new voters.

"I'm not paying too much attention to the presidential election right now because everything is still so up in the air," said Peter Palena, 20, of Wilmington, Del.

Asked about his feelings about Obama, Mike Heller, 18, said, "I see him in the news. I don't really have many feelings about him really. I guess he's doing a pretty good job."

And some college students say they aren't paying attention to politics at all.

 "Unfortunately I'm not even registered to vote," said Sheilbea Barnes, 18, of Ohio.

"We talk about elections sometimes in class, but that's the extent of my knowledge. Personally, I see politics as more of a competition," she said.