Mr Lieberman has long been considered an unconventional but plausible choice. Although Democrats have rejected Mr McCain's image as a maverick, Mr Lieberman's support for the presumptive Republican nominee has, much to the chagrin of his former colleagues, helped to boost Mr McCain's reputation as a bipartisan legislator with friends on both sides of the aisle. Mr Lieberman, a staunch supporter of Israel, could also help Mr McCain win over Jewish voters.