7-18-12  --  Former Governor Tim Pawlenty is defending Mitt Romney's refusal to release his tax returns for years prior to 2010.  On "C-B-S This Morning," Pawlenty said Romney's past income taxes should not be an issue and "there is no claim or...credible indication that Mitt Romney's done anything wrong."  Pawlenty says Romney's decision is within the range of past practice and custom.  But Texas Governor Rick Perry and two former Republican Party chairmen are among Romney supporters who believe the presumptive Republican nominee should release his tax returns.  Pawlenty is reportedly on the short list of Romney's potential running mates.