Tavits finds that, on average, shifts on pragmatic issues benefit politicians politically, whereas shifts on social issues are harmful. Since it seems like there is potential for a lot of overlap between issues designated as either "pragmatic" or "principled," the waters are muddied somewhat. But attempting to moderate or reverse one's positions on strong, clearly principled issues like abortion, gay marriage, or religion's place in public life appears to be one ticket to a lost election. If you're on the record supporting liberal social policies and you're worried about the South and Midwest, it's probably a better bet to remain passionate on the stump, while not exactly leading with those issues.
Trouble for Mitt Romney, in other words.
Matthew Yglesias is a former writer and editor at The Atlantic.