This is going to be a problem for conservatives. There are a lot of people who want to get rid Obama who would consider themselves only marginally conservative or not conservative at all. To these voters, a soft, left-leaning "Republican" like Romney is a choice they're comfortable with.
Left-leaners WILL vote Obama in November if the choice is between hard-left and soft-left. Please show me one presidential election where Liberal Lite beat Pure Liberal.