The parties fail to reach consensus on landmark legislation

In 1935, the Social Security Act had 90% Democrat support, 75% Republican. Civil Rights Act in 1964 had 60% Democrat support, 75% Republican.

Now, landmark legislation only gets passed by a single party when it has enough votes:

2010’s Affordable Care Act/ObamaCare got zero Republican votes in Congress. Trump’s 2018’s tax-reform bill got zero Democrat votes.

Ref:

• Freakonomics Radio, America's Hidden Duopoly (Podcast)