The most recent poll has Romney with 48% ‘approval’ nationally, Obama with 44%. Mixing percentages of totals from primaries is meaningless in the general election.
Right now, Romney has about half the traditional Repub voters behind him. Thats what all the primaries show. Those are hard numbers, not polls.
That equates to 1/4 of the electorate when you consider Obama has half in a 50/50 Dem/GOP split. Even if Romney does get a hard 48% of the vote (unlikely but possible) half of those people simply voted to get rid of Obama, not that they truly want or like Romney/his ideas.
Ultimately, if he wins, he will have no dem support and half of his own voters only did so out of fear/disgust.
That is not a great platform on which to build anything but a disaster.