Here's a fun chart - it's a list of all the members of the House who have scored 70% or less in a primary so far this year:
Incumbent
Party
District
%age
Notes
Inglis
(R)
SC-04
28%
TARP [RUNOFF]
Burton
(R)
IN-05
30%
Griffith
(R)
AL-05
33%
Ex-Dem [LOST]
Mollohan
(D)
WV-01
44%
Ethics [LOST]
Souder
(R)
IN-03
48%
TARP [RESIGNED]
Miller
(R)
CA-42
49%
TARP, Ethics
Kanjorski
(D)
PA-11
49%
Ethics
Lance
(R)
NJ-07
56%
Cap-and-trade
Hall
(R)
TX-04
57%
TARP, Ex-Dem, Age
Simpson
(R)
ID-02
58%
TARP
Harman
(D)
CA-36
59%
Blue Dog
Shuler
(D)
NC-11
62%
HCR
Schmidt
(R)
OH-02
62%
TARP
Kissell
(D)
NC-08
63%
HCR
McHenry
(R)
NC-10
63%
Terry
(R)
NE-02
63%
TARP
Coble
(R)
NC-06
64%
TARP, Age
Herger
(R)
CA-02
65%
TARP
Holden
(D)
PA-17
65%
HCR
Lewis
(R)
CA-41
66%
TARP, Ethics
Calvert
(R)
CA-44
67%
TARP, Ethics
Davis
(D)
IL-07
67%
Considered other office
Jackson-Lee
(D)
TX-18
67%
Rahall
(D)
WV-03
67%
Richardson
(D)
CA-37
68%
Ethics
Hill
(D)
IN-09
69%
Smith
(R)
NJ-04
69%
Cap-and-trade, TARP
Wilson
(D)
OH-06
69%
HCR
Bono Mack
(R)
CA-45
70%
Cap-and-trade, TARP
Platts
(R)
PA-19
70%
Sought Obama appointment
Granger
(R)
TX-12
70%
TARP
I've also included some notes on possible reasons for these poor performances: Dems who voted against healthcare reform, Republicans who voted for the bailout or cap-and-trade, ethical issues on either side, and a few other odds-and-ends. For a complete list of all members of Congress and their primary percentages, click here. So far, 89 (38D, 51R) incumbents have faced primaries while 141 have not (and another 13 open seats have been contested). Of those in primaries, the median vote share has been 74% (76% D, 73% R).