The biggest change Gingrich made wasn't really a policy-based one; that could easily have been reversed. The biggest change was ensuring that members of congress lived in their home districts and never interacted with opposition politicians outside of work. There can't be any rapport built up, and that makes it nearly impossible to find compromise. It has lasting effects when you only speak to people on your own side, who in turn only speak to people on their own side, ad nauseum for 20 years.
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There are a number of factors, though, making congress less centrist. Gerrymandering of districts to ensure that the only way most members will lose their seat is in a primary battle ensures that nearly everyone has to run to the far flank of their party. That's a major part of it. It's been a bigger issue for the Republicans since the tea party, but it's certainly become more significant for democrats too in recent years.