re: This is how dominant Ronald Reagan was; also showcases how terrible Obama was

OP

The original post's data is interesting but not quite useful.

We would also need to know how many seats did each start with.

For example.

If the country under Reagan, had primarily democratic control of the state houses, and that control maintained itself throughout his Tenure, then it paints a different picture.

One in which he wouldn't be considered dominate but instead, one in which he maintained the status quo.