Sen. Joe Biden -- to be well-versed on national issues , foreign policy and the social and cultural issues that have to define America . Vice presidential candidate can make lots of difference , Roland Martin says . McCain campaign has done America a disservice , he writes . He says American people want to know where she is . Thursday 's debate will be proving ground , he writes .
Vice presidential candidate can make lots of difference , Roland Martin says . McCain campaign has done America a disservice , he writes . He says American people want to know where she is . Thursday 's debate will be proving ground , he writes .