STERLING, Va. -- As a married woman, Marisa Hannum had her family's conservatism in mind when she backed Republicans in the 2008 and 2004 presidential elections. Now divorced, she is putting her own interests first as she weighs whether to vote for Democratic President Barack Obama or his Republican challenger this fall. She's an abortion opponent, worried about her finances and concerned for friends who can't find jobs. She's dumbfounded that anyone is questioning birth control access in 2012. And she has only a glimmer of an idea of how she'll vote in November. "Now I am a little bit better informed. But I am really on the fence," says Hannum, 30, an assistant restaurant manager, as she stops by the post office in this Washington suburb -- a region filled with single women that Democrats and Republicans alike are targeting. In an election year heavily focused on social issues and the economy, Democrats are trying to energize unmarried females who overwhelmingly vote for their candidates while Republicans work to peel them away. Political math tells the story of the so-called marriage gap: exit polls show that women are a majority of voters in presidential election years and about four in 10 female voters don't have a spouse. They lean more heavily Democratic than their married counterparts. But the U.S. census says about 22 percent of them are unregistered, a rich pool of potential new voters for both parties competing for the presidency and the majorities in Congress. Though single women are among the most Democratic groups in the electorate, recent political history gives Republicans hope: In the 2010 elections, Republican House candidates grabbed their highest share of women's votes in decades, at 49 percent. Single women also were hit harder than others by the recession Obama inherited. So in both parties, the race is on to woo single women, register them to vote and inspire them to show up at the polls. "There is a group of women who are up for grabs," said Democratic pollster Celinda Lake, who describes a majority of these voters as older, white and blue collar. In research she's done for the Voter Participation Center, a nonpartisan research group. Lake estimates that the share of unregistered single women could be as high as 40 percent, or 55 million people, when the group that did not answer that question on the Census is counted. Whatever the share, "their support cannot be assumed," she says. As much as 75 percent of single women vote for Democrats, so registering them to vote en masse is more beneficial for Democrats than Republicans. And, said GOP pollster Ed Goeas, single working women tend to show up to vote at some of the lowest rates of any demographic. "They are a longshot," Goeas said of single women generally. But no-longer married women like Hannum, he said, may be worth courting for the GOP in part because they tend to be more conservative than never-marrieds. The scramble for support from women generally and single women specifically accounts for the competing narratives spun by Republicans, who are focused on the economy, and Democrats targeting social issues, so far this year. Democrats have been trumpeting a "Republican war against women," a phrase coined because of GOP objections to birth control access. They have used the slogan against GOP front-runner Mitt Romney and it was the theme of a fund raising swing out West earlier this year for 11 female Democratic Senate candidates. Republicans, meanwhile, are betting that come Election Day, women - as well as men - generally will vote on Obama's stewardship of the economy. However unlike men, GOP strategists say, women have a more intimate relationship with consumer goods and are more likely to know, for example, how much the price of milk has changed, or the outlook for the family budget. It's why the party is heavily focused on the rising price of gas this year, a key pocketbook issue certain to intensify as the summer vacation season draws near. For Hannum, the economy and social issues vie for primacy on her political priority list. She's the only woman on a three-manager team at an upscale Italian restaurant in Reston. She has a red Volkswagen Jetta and bills that she alone is responsible for. She worries that gas has risen above $3.99 a gallon in Northern Virginia, and says she could not afford any kind of pay freeze or cut. "I can barely afford life as it is now," she said. So what would each party say to Hannum, and others like her? Romney's campaign responded to that question by highlighting the former Massachusetts governor's success in big business as well as his plan to rein in government spending, cut bureaucracy and restore economic growth. Hannum's take: "I'm reading about a man who's accomplished a lot," she said. But she noted that his statement did not mention women, health care or birth control. "If you're trying to win me, put something in there that has to do with me." GOP challenger Rick Santorum's appeal to Hannum was more specific. His campaign invoked her name and made note of her occupation. But Hannum said: "He won't get my vote," partly because he opposes gay marriage. Obama's campaign did not respond to Hannum. Still, after listening to both Republicans, she suggested their efforts may end up being moot. "Because of how I feel about some of the social issues, at this point, I would definitely vote Democratic over the Republicans," says Hannum, though she left open the possibility that she could be swayed. The GOP has eight months to try. ------ AP Deputy Director of Polling Jennifer Agiesta contributed to this report.