Voters in union households provided a big boost to President Obama in Ohio and Wisconsin, where key battles over public sector unions have been waged. Their strong support helped him staunch big losses elsewhere among white working-class voters.

Are the results in Ohio and Wisconsin a road map for Democrats to win back the white working-class vote across the country? The data suggest probably not. The union vote didn't make a difference among the white working-class nationally and union membership continues to erode.

White voters without college degrees made up nearly half of the total electorate in both Ohio and Wisconsin, according to exit polls, and Obama won a far greater share of these voters than he did nationally. In Ohio, 42 percent of non-college whites supported the president, as did 45 percent in Wisconsin; nationally, 36 percent backed his reelection.

Union households proved a key difference. More than one in five working-class whites in each state lives in a union household, and these voters backed Obama by double digits over Romney. By contrast, white non-college voters from non-union households supported Romney by wide margins.

There was no such union household divide at the national level. Roughly six in 10 non-college whites voted for Romney, whether they were in a union household (59 percent) or not (61 percent).

One reason for the big differences in Ohio and Wisconsin may be the hotly contested battles between unions and Republican governors in the past two years. Wisconsin’s unions mounted a massive and ultimately unsuccessful effort to recall Gov. Scott Walker after he curbed collective bargaining rights for government workers. Walker is largely unpopular among those in union households in Wisconsin according to the state exit poll, with a 2 to 1 negative to positive job approval rating. Nearly six in 10 members of non-union households approve of his job performance.

Last year, unions led a successful campaign in Ohio to repeal a law signed by Gov. John Kasich that limited collective bargaining rights. Both campaigns may have served to unite union voters in opposition to Republicans.

Of course, unions may not be able to save Democrats everywhere. At the national level,  just 18 percent of voters are union members themselves or live in a house with a member. That’s down six percentage points since 2004 and the lowest level in exit polls back to 1972. In Ohio and Wisconsin, the numbers also fell to new lows, with just over two in 10 voters living in a union household in both states.