President Barack Obama's camp seized on "outrageous" comments about rape by one of Mitt Romney's fellow Republicans, hoping to carve out a decisive edge among women voters.
Obama is barnstorming the country in what he hailed as an eight-state, 40-hour "campaign marathon extravaganza," trying to shore up his re-election bid by building a firewall across the key battlegrounds.
Romney was on similar territory, telling voters in western swing state Nevada, where Obama was due later, that the president's campaign in the neck-and-neck election boiled down to four words: "More of the same."
And the Republican made a bold prediction of victory on November 6, despite signs that Obama holds a slight edge in the clutch states that will send one man to the 270 electoral votes needed for the presidency.
"The Obama campaign is slipping because it can't find an agenda to help the American families," Romney said in Cedar Rapids, Iowa, hours after Obama had left the state.
"I'm optimistic. I'm optimistic, not just about winning... We are going to win by the way..." Romney said.
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But the Republican's effort to focus on Obama's economic record was complicated by a new row over comments by Republican Senate candidate Richard Mourdock, once again throwing a spotlight on his party's stance on women.
Mourdock said that pregnancy caused by rape was "something God intended to happen" and Obama aides quickly highlighted the fact that Romney, who it says backs 1950s style social policies, had endorsed the Indiana candidate.
"The president felt those comments were outrageous and demeaning to women," Obama spokeswoman Jen Psaki said, adding that it was "perplexing" that Romney would not take down an ad featuring him endorsing Mourdock.
The row put Romney in an awkward spot with women voters, who already favor Obama in larger numbers and whose support could prove decisive in knife-edge races on November 6.
Romney enjoys strong support among evangelical voters and social conservatives, who oppose abortion as an article of faith and who form an important part of his base in battlegrounds like Ohio.
A new poll by Time magazine in the Midwestern Rust Belt state released yesterday put Obama up by five points.
Many analysts think victory in Ohio would be enough to put Obama over the top in his quest for re-election.
There were also signs that Romney's momentum of the last few weeks was abating. The Republican led a RealClearPolitics average of national polls by just 0.6%.