Why is there gridlock in Congress?

There is a simple reason for gridlock in Congress. There is no overlap in points of view. Compare the 90th Congress with the 110th Congress. This is a 40 year difference that seems like from another era. This graph normalizes the voting record of Democrats and Republicans and shows that there was a degree of overlap between the two parties 40 years ago. More recently, there is almost no overlap. The parties have become more polarized.  This causes gridlock. The only way out of the gridlock is that there has to be politicians who are willing to move outside party norms. Under current conditions, this is unlikely until we have a crisis.