DES MOINES, Iowa (September 27, 2012)--Republican presidential challenger Mitt Romney is struggling in swing-state Iowa at a perilous point, just as voters start casting early ballots in the presidential race Thursday.

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 in Iowa is so wide that it has prompted grumbling among state Republicans who fault Romney for failing to take advantage of Mr. Obama's standing, which has been weakened in the four years since Iowa launched his bid for the White House.

Iowa is hardly the largest prize in the race for the 270 Electoral College votes, but its six votes could be pivotal if the race is close.