A more interesting question, in which districts did a Green or other left leaning third party candidate get more votes then the margin between a winning Republican and losing Democrat?
And in which districts did a Libertarian, Constitution, Tea Party candidate or other Right leaning third party candidate get more votes then the margin between a winning Democrat and losing Republican?
From 2010:
AZ-08
Gabrielle Giffords (D) 48.8%
Jesse Kelly (R) 47.3%
Steven Stoltz (L) 3.9%
CA-11
Jerry McNerney (D) 48.0%
David Harmer (R) 46.9%
David Christensen (AI) 5.2%
IL-08
Joe Walsh (R) 48.5%
Melissa Bean (D) 48.3%
Bill Scheurer (G) 3.2%
IN-02
Joe Donnelly (D) 48.2%
Jackie Walorski (R) 46.8%
Mark Vogel (L) 5.0%
MO-03
Russ Carnahan (D) 48.9%
Ed Martin (R) 46.7%
Steven Hedrick (L) 2.8%
Nick Ivanovich (C) 1.6%
NY-23
Bill Owens (D) 47.5%
Matt Doheny (R) 46.4%
Doug Hoffman (Cons) 6.1%
VA-11
Gerry Connolly (D) 49.2%
Keith Fimian (R) 48.8%
Chris DeCarlo (I) 0.8%
David Dotson (L) 0.6%
David Gillis (IG) 0.4%
I excluded the races with independents (since there's no telling what their political views were) and the Independence Party in Minnesota.
