Mitt Romney has long hailed his background as a successful business executive to convince Republican primary voters that he is best suited to lead the country’s economic turnaround. But now an increasing number of Romney’s competitors are trying to this perceived strength into a weakness. Former Utah Governor Jon Huntsman, referring to Romney’s work running Bain Capital, which specialized in leveraged buyouts of existing companies, said, “Private equity, like Bain, traditionally has not been famous for expanding the economic base.’’