Fueled almost exclusively by a huge jump in support by women under 50, President Obama has taken a sizable lead in the latest Swing State Poll by Gallup.

USA Today:

In the fifth Swing States survey taken since last fall, Obama leads Republican front-runner Mitt Romney 51%-42% among registered voters just a month after the president had trailed him by two percentage points.

The biggest change came among women under 50. In mid-February, just under half of those voters supported Obama. Now more than six in 10 do while Romney's support among them has dropped by 14 points, to 30%. The president leads him 2-1 in this group.

Romney's main advantage is among men 50 and older, swamping Obama 56%-38%.

Republicans' traditional strength among men "won't be good enough if we're losing women by nine points or 10 points," says Sara Taylor Fagen, a Republican strategist and former political adviser to President George W. Bush. "The focus on contraception has not been a good one for us ... and Republicans have unfairly taken on water on this issue."

In the poll, Romney leads among all men by a single point, but the president leads among women by 18. That reflects a greater disparity between the views of men and women than the 12-point gender gap in the 2008 election.

Obama campaign manager Jim Messina says Romney's promise to "end Planned Parenthood" - the former Massachusetts governor says he wants to eliminate federal funding for the group - and his endorsement of an amendment that would allow employers to refuse to cover contraception in health care plans have created "severe problems" for him in the general election.

"Romney's run to the right may be winning him Tea Party votes," Messina said in an interview, but he says it's demonstrated that "American women can't trust Romney to stand up for them."

The states surveyed were Colorado, Florida, Iowa, Michigan, Nevada, New Hampshire, New Mexico, North Carolina, Ohio, Pennsylvania, Virginia and Wisconsin.

A Romney campaign spokesman says that the gender gap will narrow before election day. It better. An 18 point spread in these vital states between Obama and Romney among women would mean curtains for the GOP nominees campaign.

The gender gap hasn't been much of a factor until 2008 when John McCain lost women by 12 points. This time, it appears the Democratic narrative about a GOP "war on women" may be resonating with voters. The partisan divide is even more telling. Women self identify as Democrats by a 41-24 margin. Men favor Republicans 27-25.