AMES, Iowa -- If President Obama doesn't win a second term next Tuesday, he won't have trouble finding the root problem. As the president likes to say, it's simple math: Waning support among white voters could torpedo his re-election bid.

America's first black president, who rode a wave of enthusiasm from both Democrats and Republican-leaning independents four years ago, faces a far more tenuous path to victory this time around.

Polls show Obama winning less than 40 percent of white voters and having to make up that gap by mobilizing minority voters in force. The reasons for that sagging support are obvious here in Iowa, one of the nation's whitest states, where voters helped propel Obama to the Democratic nomination and ultimately the White House in 2008 but now aren't so sure about him.

Dozens of voters interviewed across the Hawkeye State said that while many still personally like the president, they are disappointed with his first-term performance and his inability to turn around an ailing economy.

"He's a good father, a good person," Delton Ziesch, 63, a janitor from Des Moines, said. "But his policies are terrible. People flocked to him four years ago. No more."

The president's problems among white voters aren't the product of racial animosity, voters and analysts insist, pointing to Obama's overwhelming support in the state four years ago.

"It's twofold," Dennis Goldford, a political scientist at Drake University in Des Moines, said. "It's a competence argument and the belief among some that Obama does not share their values -- the race component is a fringe element."

White voters' support for Obama isn't much lower than it was for Democratic nominees John Kerry, who won 41 percent of that vote in 2004, or Al Gore, who got 42 percent in 2000. But both of them lost. And the fact that Romney enjoys the support of 60 percent of white voters -- a benchmark not achieved since President Reagan in the 1980s -- makes the gap more problematic.

"Obama is ahead, but Romney is closing," David Yepsen, a longtime Iowa political reporter and director of the Paul Simon Public Policy Institute, said. "And yes, the white vote is a major issue for Obama."

The Obama campaign counters that the president's broad appeal is self-evident and that the Midwest is more receptive to the incumbent than states with similar demographics.

"Iowans know President Obama; he has a history with them," an Obama campaign official told The Washington Examiner. "You should be focusing on Mitt Romney's utter lack of appeal to a diverse range of voters."

Indeed, despite Romney's deep support among whites, blacks are almost unanimously backing Obama and so are the overwhelming majority of Hispanics, the nation's fastest growing voting bloc.

But here in Iowa, even some Obama supporters doubted the president could win without more white voters.

"The Midwest has more of a culturally conservative, elderly type of population," said Becky McDowell, of Osceola, who's backing Obama. "I don't feel great about it."

Dave Nelson, 58, an information technology worker from Garden City, says it's nothing personal.

"We don't blame Obama for all our problems," Nelson said. "But anybody with common sense can see he didn't accomplish what he promised."