Darrell Issa is the latest in a series of House Republicans to depart Congress after this term, he announced Wednesday. His seat in southern California is particularly vulnerable for the party in 2018, as Hillary Clinton won his district by 7.5 points.

Outlier check: There are now 28 retiring representatives. The average number over the last five election cycles has been 23. Over that time, there has been more attrition from Republicans than from Democrats, however, the 3-to-1 ratio of retiring Republicans to Democrats this cycle is considerable.

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: