(CNN) - Former GOP presidential candidate Rick Santorum offered no insight into his own political future in a Friday CNN interview, but did offer his thoughts as to why the Republican nominee lost to President Barack Obama on Tuesday. "What Mitt Romney, in my opinion, didn't do was go out and vigorously defend the beliefs that he said he espoused and didn't go on the offense," Santorum said in an interview to air Friday on CNN's "Piers Morgan Tonight." "And when you're playing defense, which is what I believe the campaign was doing and Republicans were doing generally throughout the...