Well, for starters, Romney’s record on women’s issues and gay issues are two big openings Obama has been pounding Romney on. Also the fact Romney believes in trickle down economics. And it’s pretty legitimate to attack Bain Capital for being a driving force in outsourcing american jobs; nothing illegal there, but Mitt clearly believes in outsourcing, something a lot of Americans aren’t fans on. These are legitimate policy differences.
I do think Romney should be more open in saying “I didn’t write the tax code. Like most American families, we maximized our deductions while following the laws as they are written”. But I think Mitt needs to be more open and honest about a lot of things.