This doesn’t sound like an attack that would hurt Santorum in the general election. Unions are doing just fine in Ohio, and down but not out in Wisconsin. Heck, Newt has already proven himself too conservative for some voters in the primary (NH, FL). Sad but true. I’m afraid this attack by Newt could backfire, and just help Rick in the Midwest where they already seem to like his corporate welfare proposal for the manufacturing industry.
I don't believe it's a case of Newt being "too conservative". It's more like Newt being "too unstable".
There is a thing called "Presidential Temperament". Whether Newt has it or not is a very open question.