Rick Santorum's 15-point lead shrinks to 4
                                
                                
                                    (Newser) -
                                    Last week, Rick Santorum led Mitt Romney in the Michigan race  by 15 points ; now, that lead is down to just four points,  Public Policy Polling  finds. Some 37% of voters say they support Santorum, compared to 33% for Romney; Ron Paul follows with 15%, while Newt Gingrich stands at...