There's another issues, both parties are courting the more extreme views within their parties.

That is, the Democrats are looking further left/liberal, and the Republicans are looking more right/conservative.

Neither is looking after the centre, they only seek to appease the more vocal within their ranks... the extremists.

Typically when the pendulum swings things average out, but politicians have learned over the past several decades that if they want to gain 10 miles of political position they should negotiate for 100 miles from the outset and beat the other party into submission before settling on 20 miles (everyone's a winner).

The entire system seems to promote seeking an extreme position even if such a position isn't desired by anyone.