GOP elites, the base, and the GOP brand
What Mitt has been trying to do of late is akin to asking John Majors' cronies to attack Lady Thatcher's reputation on his behalf.
Beltway insiders may like to point out that after Newt was ditched the Republicans remained in control Congress for several years and the daily drama quotient on Capitol Hill was much reduced. What many conservative voters outside the beltway tend to remember is quite different: that after Newt, politics as usual Republicans began spending as if there were no tomorrow, conservative reforms came to a halt and institutional corruption began to once again take hold.
It wasn't Newt that damaged the brand. It was the far lesser men that replaced him, men who are on Romney's side such as that son of Illinois' crony capitalist politics, Dennis Hastert.