Outlier check 2: 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 21 Republicans is 9.4.

Note: This list includes retirements and resignations, not those seeking or appointed to a higher office.

A look at the 21 departing Republicans...

Darrell Issa of California:

• Date announced: Jan. 10
• Terms: 9 terms
• 2016 margin of victory: 0.6 points
• 2016 presidential: Clinton by 7.5 points

Ed Royce of California (Chair of Foreign Affairs Committee):

• Date announced: Jan. 8
• Terms: 13 terms
• 2016 margin of victory: 14 points
• 2016 presidential: Clinton by 9 points

Gregg Harper of Mississippi (Chair of House Administration Committee):

• Date announced: Jan. 4
• Terms: 5 terms
• 2016 margin of victory: 36 points
• 2016 presidential: Trump by 25 points

Bill Shuster of Pennsylvania (Chair of Transportation & Infrastructure Committee) :

• Date announced: Jan. 2
• Terms: 9 terms
• 2016 margin of victory: 27 points
• 2016 presidential: Trump by 43 points

Blake Farenthold of Texas:

• Date announced: Dec. 14, 2017 (retiring in scandal)
• Terms: 4 terms
• 2016 margin of victory: 23 points
• 2016 presidential: Trump by 24 points

Trent Franks of Arizona:

• Date announced: Dec. 7, 2017 (resigned in scandal)
• Terms: 7 full terms
• 2016 margin of victory: 37 points
• 2016 presidential: Trump by 21 points

Joe Barton of Texas:

• Date announced: Nov. 30, 2017
• Terms: 17
• 2016 margin of victory: 19 points
• 2016 presidential: Trump by 12 points

Bob Goodlatte of Virginia (Chair of Judiciary Committee):

• Date announced: Nov. 9, 2017
• Terms: 13
• 2016 margin of victory: 34 points
• 2016 presidential: Trump by 25 points

Ted Poe of Texas:

• Date announced: Nov. 7, 2017
• Terms: 7
• 2016 margin of victory: 25 points
• 2016 presidential: Trump by 9 points

Frank LoBiondo of New Jersey:

• Date announced: Nov. 7, 2017
• Terms: 12
• 2016 margin of victory: 22 points
• 2016 presidential: Trump by 5 points

Lamar Smith of Texas (Chair of Science, Space & Technology committee):

• Date announced: Nov. 2, 2017
• Terms: 15
• 2016 margin of victory: 31 points
• 2016 presidential: Trump by 10 points

Jeb Hensarling of Texas (Chair of Financial Services committee):

• Date announced: Oct. 31, 2017
• Terms: 8
• 2016 margin of victory: 61 points
• 2016 presidential: Trump by 28 points

Pat Tiberi of Ohio:

• Date announced: Oct. 19, 2017
• 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, 2017
• Terms: 7 full terms
• 2016 margin of victory: uncontested
• 2016 presidential: Trump by 20 points

Dave Trott of Michigan:

• Date announced: Sept. 11, 2017
• Terms: 2
• 2016 margin of victory: 13 points
• 2016 presidential: Trump by 5 points

Charlie Dent of Pennsylvania:

• Date announced: Sept. 7, 2017
• Terms: 7
• 2016 margin of victory: 20 points
• 2016 presidential: Trump by 8 points

Dave Reichert of Washington:

• Date announced: Sept. 6, 2017
• Terms: 7
• 2016 margin of victory: 20 points
• 2016 presidential: Clinton by 3 points

John J. Duncan Jr. of Tennessee:

• Date announced: July 31, 2017
• Terms: 15
• 2016 margin of victory: 51 points
• 2016 presidential: Trump by 35 points

Ileana Ros-Lehtinen of Florida:

• Date announced: April 30, 2017
• Terms: 14
• 2016 margin of victory: 10 points
• 2016 presidential: Clinton by 20 points

Lynn Jenkins of Kansas:

• Date announced: Jan. 25, 2017
• Terms: 5
• 2016 margin of victory: 28 points
• 2016 presidential: Trump by 19 points

Sam Johnson of Texas:

• Date announced: Jan. 6, 2017
• Terms: 13
• 2016 margin of victory: 27 points
• 2016 presidential: Trump by 14 points