The sharpest increase was there in the early 1990s, one of the only periods of unified Democratic control of the federal government, and a large majority of state governments as well. Its sharpest decline — still pretty modest in context — was in the latter years of George W. Bush, and it rose again sharply under Obama. It didn’t really matter which party was in charge, inequality has gone up.
I’ve noted in other stories that that “sharpest increase” also happened while Bush I and Clinton were RAISING taxes.
Which negates the commonly held myth that income inequality can be rectified using the income tax system.