Have you looked at the dates on the chart?
https://www.statnews.com/wp-content/uploads/2018/10/CDC-Over...
https://www.statnews.com/wp-content/uploads/2018/10/CDC-Over...
2016: 246-194 Republican
2014: 247-188 Republican
2012: 234-201 Republican
Six year incumbency.
2016: 52-46 Republican
2014: 54-44 Republican
2012: 53-45 Republican
2010: 51-47 Republican
8 years incumbency