DES MOINES, Iowa — 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.