On Tuesday, voters in Indiana and North Carolina will go to the polls to vote in what could be one of the most significant days of the Democratic presidential race. But in Indiana, the Wall Street Journal suggests, it might not be Democrats who matter most to the final results.

Indiana's primary is open, which means that Republicans can cross over if they wish and vote in the Democratic primary instead. And they may have reason to -- besides the general swing from Republican to Democrat lately, there's just not as much reason to vote in the Republican primary now, since that party's presidential race is over and there aren't many big local down-ticket races. With that in mind, the WSJ reports that the state Democratic Party's chairman estimates that Republicans could constitute as much as 15 percent of turnout for the Democratic primary; officials with Barack Obama's campaign put that number at about 5 percent.

There are reasons to think either Democratic candidate could be the beneficiary of Republican votes. For Hillary Clinton, there's the possibility that Rush Limbaugh's "Operation Chaos," intended to prolong the Democratic race by giving Clinton Republican votes, could help her. The Obama camp, meanwhile, has been reaching out to Republicans in the state, and will even be rolling out three prominent state Republicans who are supporters of his campaign.