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(CNN) - In campaign contests so far, Barack Obama has polled the best among black, more wealthy and educated voters and college students, while rival Hillary Clinton has been able to count on women, low-income voters and blue-collar workers.
But in early exit polls tonight, Obama held Clinton to a virtual tie among Wisconsin Democratic primary voters who said they have a union member in their household - 50 percent for Clinton to 49 percent for Obama - and actually edged her among women, 51 percent to 49 percent.
Clinton held a narrow advantage over Obama among Catholic poll respondents - who made up 43 percent of voters interviewed - 51 percent to 48 percent. She also held narrow leads among voters with only a high school education, people 60 or older and those making between $15,000-$30,000 a year.
But Obama kept those margins close and took easy wins among his traditional base of supporters.
Among voters 49 years old and younger he had a significant 64-39 percent advantage over Clinton. College-educated voters, who made up 72 percent of those polled, favored him 59 percent to 39 percent.
Obama had a slight edge among voters who called themselves Democrats - 50 percent to 49 percent - but overwhelmingly topped Clinton among the 27 percent of respondents who called themselves independents, taking 63 percent of their votes to Clinton's 36 percent.