Massachusetts' critical seat

Today's election will fill the seat of the late senator Ted Kennedy but in the bluest of blue states, polls show the state's attorney general, Democrat Martha Coakley, trailing her Republican challenger, State Senator Scott brown. A GOP win would mean the Democrats will lose their filibuster-proof 60-seat majority in the Senate and jeopardize President Obama's health care reform plan. CNN senior political analyst and former presidential adviser, David Gergen spoke with CNN's John Roberts Tuesday.