A wonderful bit of political nerd playdough here. I’m warning political junkies now: This thing can eat up time messing with it!
In the US, gerrymandering, or redistricting, as it’s called, is in the hands if the state legislatures and is done with such precision as to make the vast majority of seats (Because of individual voter party registration: A bizarre concept to Europeans!) either solidly Republican or solidly Democratic. It’s shockingly corrupt to an Orwellian degree, and means that general elections don’t matter in huge tracts of the US, as far as legislative seats are concerned. On top of that, it means that the real election is decided in the primaries, which means that the winners tend to be either extreme liberals or extreme conservatives, and you end up with a polarised political system where centrist voters are almost completely excluded.
The funny thing is, the Irish electoral system, which causes problems of its own in Ireland, would be ideal for resolving most of these problems.