My wife is a nationally recognized expert in elections in the US. The combination of FPTP and politically controlled district geometry (gerrymandering) explicit

My wife is a nationally recognized expert in elections in the US. The combination of FPTP and politically controlled district geometry (gerrymandering) explicitly creates a brittle system that engenders extremism. It's well understood to be both the cause and a reinforcement mechanism. The mechanism we have now was left in place in the early 19th c. explicitly to allow a small minority to be able to control their individual states. The main change since then has been cross-state unification of the party system. To give an example: here, in Texas, the most volatile Federal district was won by a representative who received only 10% of the votes in his district. Some districts were won by reps with as few as 1% of the total votes (that's total turnout). (This is due to the primary mechanism and gerrymandering.) If you can win by harnessing just 10% of the electorate, you're shopping around for the ironclad voters, and they tend to have weird views (left or right).