Elliott Abrams blasts Gingrich's self-image as one of Reagan's closest allies:

The best examples [of Gingrich attacking Reagan] come from a famous floor statement Gingrich made on March 21, 1986. This was right in the middle of the fight over funding for the Nicaraguan contras; the money had been cut off by Congress in 1985, though Reagan got $100 million for this cause in 1986. Here is Gingrich: “Measured against the scale and momentum of the Soviet empire’s challenge, the Reagan administration has failed, is failing, and without a dramatic change in strategy will continue to fail. . . . President Reagan is clearly failing.” Why? This was due partly to “his administration’s weak policies, which are inadequate and will ultimately fail”; partly to CIA, State, and Defense, which “have no strategies to defeat the empire.” But of course “the burden of this failure frankly must be placed first on President Reagan.” 

Jonah Goldberg can't imagine why Romney isn't bringing this up more. Doug Mataconis remembers when Republicans weren't afraid to criticize Reagan:

Gingrich’s attacks on Reagan were actually quite common among members of the hard-line right in the late 80s, especially once the President began pursuing a new relationship with the Soviet Union upon the rise to power of Mikhail Gorbachev. I recall reading some of that criticism the pages of National Review itself at the time, and hearing it on the airwaves from the likes of Rush Limbaugh. Reagan was a patsy, they said. He was letting himself be deceived by a man with a nice smile who was still, at heart, the same kind of Communist that his predecessors were. Some conservatives were even suggesting in the late 80s that Reagan’s openings to the Soviet Union and willingness to negotiate were signs of oncoming senility.