plumb

Plumb = vertical. 

When a building or a wall leans to the left or to the right, then it isn't "right"; it's not plumb or vertical.

The same works for government. When government leans too far to the left or to the right, it needs to be straightened.

Elections are about straightening leaning government. When government changes from Democratic party control to Republican party control, then the left-leaning government gets straightened. The opposite is true when a Republican controlled government loses an election.

This is the way that our two-party system of government works.