There are now 12 Republicans departing in 2018 and just one Democrat. In addition, Jason Chaffetz resigned his seat in June, and his replacement is being elected Tuesday.

• Outlier check 1: According to Brookings, the average terms served for retiring members has hovered around 8 over the last 40 years, but dropped to 5 in the 2016 cycle. The average among these 12 Republicans is 9.5.
• Outlier check 2: The number to watch for to help determine if this trend is notable is 23. That's the average number of retiring representatives over the last five election cycles. Over that time, there has been more attrition from Republicans than from Democrats. However, the 12-to-1 ratio of retiring Republicans to Democrats is a considerable disparity.

A look at the 12 departing Republicans...

Frank LoBiondo of New Jersey:

• Date announced: Nov. 7
• Terms: 12
• 2016 margin of victory: 22 points
• 2016 presidential: Trump by 5 points

Lamar Smith of Texas:

• Date announced: Nov. 2
• Terms: 15
• 2016 margin of victory: 31 points
• 2016 presidential: Trump by 10 points

Jeb Hensarling of Texas:

• Date announced: Oct. 31
• Terms: 8
• 2016 margin of victory: 61 points
• 2016 presidential: Trump by 28 points

Pat Tiberi of Ohio:

• Date announced: Oct. 19
• Terms: 9
• 2016 margin of victory: 37 points
• 2016 presidential: Trump by 11 points

Tim Murphy of Pennsylvania (resigned in scandal):

• Date announced: Oct. 5
• Terms: 7 full terms
• 2016 margin of victory: uncontested
• 2016 presidential: Trump by 20 points

Dave Trott of Michigan:

• Date announced: Sept. 11
• Terms: 2
• 2016 margin of victory: 13 points
• 2016 presidential: Trump by 5 points

Charlie Dent of Pennsylvania:

• Date announced: Sept. 7
• Terms: 7
• 2016 margin of victory: 20 points
• 2016 presidential: Trump by 8 points

Dave Reichert of Washington:

• Date announced: Sept. 6
• Terms: 7
• 2016 margin of victory: 20 points
• 2016 presidential: Clinton by 3 points

John J. Duncan Jr. of Tennessee:

• Date announced: July 31
• Terms: 15 full terms
• 2016 margin of victory: 51 points
• 2016 presidential: Trump by 35 points

Ileana Ros-Lehtinen of Florida:

• Date announced: April 30
• Terms: 14 full terms
• 2016 margin of victory: 10 points
• 2016 presidential: Clinton by 20 points

Lynn Jenkins of Kansas:

• Date announced: Jan. 25
• Terms: 5
• 2016 margin of victory: 28 points
• 2016 presidential: Trump by 19 points

Sam Johnson of Texas:

• Date announced: Jan. 6
• Terms: 13 full terms
• 2016 margin of victory: 27 points
• 2016 presidential: Trump by 14 points