DES MOINES, Iowa (AP) — Republican Mitt Romney is struggling in swing-state Iowa at a perilous point: just as voters here start casting early ballots in the presidential race.

President Barack Obama has a clear lead in Iowa opinion polls, helped by the fact that the state’s economy is far more robust than other battleground states. The president’s polling edge is so wide it has prompted grumbling among Iowa Republicans who fault Romney for failing to take advantage of Obama’s standing, which had been weakened in the four years since Iowa launched his bid for the White House in 2008.

“There still is time to win, but we are in the fourth quarter,” said Nick Ryan, a veteran Iowa Republican strategist who was a top adviser to Pennsylvania Sen. Rick Santorum’s caucus campaign.

Iowa is hardly the largest prize in the race for 270 Electoral College votes. But the six it offers could be pivotal if the race is close.

Iowans on Thursday can begin voting in person at early voting sites and returning absentee ballots they’ve requested by mail or in person. Iowa Republicans are mindful that the perception of Romney in deep trouble could sway voters already casting ballots — or dissuade volunteers from encouraging backers to turn out at the polls.

The state knows Romney and Obama well; both competed here in 2008. And Romney came close to winning its caucuses in January.

“A lot of people I know are excited about Romney,” said Susan Geddes, a Republican from Indianola, just south of Des Moines. “And a lot of people I talk to are like me, and just want it over with.”

Since locking up the GOP nomination in the spring, Romney has visited the state six times and has poured $8 million into television advertising here. GOP-leaning groups have tried to help, spending $20 million in TV ads criticizing Obama. But Romney hasn’t been to the state since Sept. 7, when he made a trip to the Republican-heavy northwest. And he has paid scant attention to the blue-collar voters along Iowa’s eastern edge, where unemployment is running higher than in the state overall and where he needs a big turnout to overtake Obama.

The Republican’s team insists that he hasn’t given up on the state and that he and his running mate, Paul Ryan, plan to spend more time in Iowa in the final weeks of the campaign.

“You’re going to see the governor and Paul Ryan talking a lot directly to voters, having more opportunities to do that,” campaign spokeswoman Sarah Pompei said.

Aides argue that Romney has built a more sophisticated voter-contact system than Republican John McCain did in 2008, when Obama carried Iowa by 9 percentage points. And although Romney has only 14 staffed state campaign offices, compared with Obama’s 67, Republicans say they have made more than 1 million contacts with voters by telephone and in person.

If the polls are right, the GOP ticket has a lot of ground to make up.

A Wall Street Journal/NBC News/Marist Poll taken last week found Romney trailing Obama by 8 percentage points, a finding that mirrored recent internal polls from Democrats and Republicans alike. The poll also found that only 40 percent had positive feelings about Romney, down from 43 percent in May. Conversely, Obama saw his favorability rating improve to 53 percent from 48 percent over that same period.

Those figures illustrate why Obama’s campaign is increasingly confident about its Iowa prospects even as aides say they expect the race to tighten somewhat as undecided voters focus on the election.

Democrats say Obama has benefited from his Iowa strategy of blanketing the state with eight presidential visits ahead of early voting. Obama hoped that his frequent visits, as well as constant appearances by Vice President Joe Biden and first lady Michelle Obama, would help him build a lead over Romney ahead of Election Day, when Republicans traditionally have had an edge.

Obama focused his attention on more populous and politically diverse eastern Iowa. The small and medium-sized cities, many with struggling manufacturing sectors, were friendly territory for Romney in the Iowa caucuses but now show him trailing Obama in internal polling. Obama’s three-day, statewide trip in August touched down in less-traveled cities in north- and south-central Iowa. He also made a well-publicized visit to the Iowa State Fair in Des Moines.

The president also has run more than $20 million in ads, including many that characterize Romney and his positions as those of a wealthy, detached former business executive. Obama allies also have spent roughly $3 million in advertising.

Obama aides say Romney’s criticism of Obama’s handling of the economy has been less effective here than it has been in states such as harder-hit Florida and Nevada. In August, Iowa unemployment was 5.5 percent, up from July but far below the national average of 8.1 percent.

But Obama aides also say Romney hasn’t made as much of an effort to build a personal connection with voters in a state where face-to-face campaigning is key, and they say his comment about 47 percent of Americans who don’t pay federal income tax has been problematic.

“He doesn’t think poor people are his problem,” Oskaloosa Democrat Pam Douglas said. “They are his problem if he wants to be president.”

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Associated Press writer Julie Pace in Chicago contributed to this report.