In many ways -- particularly morally -- Gingrich proved himself the equal of Bill Clinton ... except politically, in which arena he proved to be an empty suit who was incapable of putting his words into action. Gingrich's political stupidity played a large role in getting Clinton re-elected in '96.
Even if there's truth to some of what he says, I can't help but seeing it mostly as a self-serving attempt by Gingrich to try to stake out a niche in the runup to the 2008 presidential race.
1) every item in the Contract with America except term limits passed the house.
2) every item in the Contract except the two constitutional amendments became law within two years in some form.
3) the "embarassing" political losses of which you speak only occured in the Nov. 98 election -- and he had a lot of help in bringing those about... there is plenty of blame to go around on that one.
4) the drift of which you speak only came about, IMHO, after Gingrich was gone and Tom DeLay decided to spend his way into a permanent majority.
-- I could go on, but that's enough for a start