From an interview on FOX as transcribed here by The Washington Post:
O’Reilly: Is he a socialist?
Romney: You know, I prefer to use the term that he’s just over his head. ... I consider him a big-government liberal Democrat. I think as you look at his policies, you conclude that he thinks Europe got it right and we got it wrong. I think Europe got it wrong. I think Europe is not working in Europe. And I’ll battle him on that day in and day out. But I’m probably not going to be calling him names so much as calling him a failure.