I think Mitt Romney is in an interesting position now regarding general election strategy: he is deeply distrusted by his base and he already has a reputation as changing positions to suit whatever electorate he is courting. I don’t know if he’ll ever be able to excite the base beyond the level of enthusiasm they will have for getting Obama out regardless of who replaces him.
He has seemed in the past couple of weeks to be transitioning to a messaging more along the lines of “are you better off today than you were 3 years ago?” that seems more likely to appeal to moderates. He has also seemed recently to be taking moderate positions on new issues: saying he would not attempt to repeal the Lily Ledbetter Fair Pay Act and saying that he supports the extension of low interest rates for student loans.
Generally, I think that as we get closer to November Romney will have to define himself and his vision for the country in more explicit terms than “I am a businessman” and saying that the President is in over his head. The media will also have to hold Romney more accountable in the general election and question more harshly his claims about Obama’s apologizing for America and the phantom devastation Obamacare is going to bring to the country.