One in four registered voters may be persuadable in the 2012 presidential election - rich pickings if either Barack Obama or newly minted GOP nominee Mitt Romney can win their support. But doing so may be a challenge, requiring both subtle and substantive political persuasion.

That's because persuadable voters, as identified in this analysis for ABC News, are less apt to be ideologically committed ones, and more likely to take middle-ground rather than strongly held positions on issues such as Obama's job performance, Paul Ryan's Medicare plan and their own partisan views.

See PDF with accompanying table here.

Among registered voters who "strongly" approve or strongly disapprove of Obama's work in office, for instance, about two in 10 appear persuadable. Among those who "somewhat" disapprove, however, the level of persuadability jumps to 42 percent in the latest ABC News/Washington Post poll.

If that's an avenue of persuasion particularly for Romney, Obama may find opportunities of his own. This analysis, produced for ABC by Langer Research Associates, finds that 29 percent of Romney's current supporters are persuadable, as are 24 percent of Obama's.

This evaluation uses a method of identifying persuadable voters based on a model of anxiety and information-gathering developed by George Marcus, a political science professor at Williams College, and his colleagues Michael MacKuen of the University of North Carolina and W. Russell Neuman of the University of Michigan. Their work indicates that voters who are anxious about the candidate they support, and who are seeking information about the candidates' positions, are more open to changing their position - in a word, persuadable. The candidate who makes the best argument has a shot at winning their vote.

One element of persuadability, anxiety, is significant: In the new ABC/Post poll, 53 percent of Obama's backers say that regardless of their supporting him, they're anxious about how he'd perform in a second term as president - and even more of Romney's supporters, 62 percent, are anxious about their man. Four in 10 overall also say they're interested in more information about the candidates. And 25 percent meet both those conditions: anxious about their candidate, and looking for more information.

There are some differences among groups. Age is one, with senior voters least apt to be persuadable -18 percent of those older than 65 are persuadable, compared with 28 percent of adults 18 to 64. There's also a regional effect, with persuadability higher in the Midwest (31 percent) and lowest in the Northeast (18 percent).

Attitudinal measures are particularly interesting. Moderates and "somewhat" conservatives are more apt to be persuadable than liberals or "very" conservatives (29 vs. 21 percent), evidence that less ideologically committed voters are more persuadable ones. In another example, persuadability is higher among people who are either somewhat opposed to the Tea Party movement, or somewhat supportive of it, compared with "strong" supporters or opponents.

In a regression analysis, holding other factors constant, several emerge as independent predictors of persuadability. These include strong sentiment on the Tea Party, strong sentiment on Obama and strong opposition to Ryan's plans for Medicare, all negatively predicting being persuadable; and having lower incomes or favoring government spending to try to create jobs, both positive predictors of being persuadable.

This measure of persuadability is a different one from the more traditional self-assessment, obtained by asking people who support a candidate if they might change their minds. That produces a lower estimate of persuadable voters - 15 percent, rather than 25 percent using the anxiety/information-seeking measures - and perhaps a less accurate one, given research showing that while people can express their attitudes well, they have more difficulty self-assessing where those attitudes come from, or might go.