One of the under-reported factors for the Democratic victories in 2006 was the spoiler effect that the Libertarian Party played. Here are races in which the Libertarian vote was larger than the Democratic margin of victory:
Missouri Senate
McCaskill (D) 1,047,049 50
Talent (R) 1,001,238 47
Gilmour (L) 47,504 2
Montana Senate
Tester (D) 198,302 49
Burns (R) 195,455 48
Jones (L) 10,324 3
That's control of the Senate right there. And in the House there was at least one race in which Libertarians helped deliver a seat to Democrats:
IN-09
Hill (D) 110,185 50
Sodrel (R) 100,503 46
Schansberg (L) 9,920 4
In several other contests, the Libertarians helped give us tight, tight, tight races:
CA-04
Doolittle (R) 104,746 49
Brown (D) 97,217 46
Warren (L) 10,668 5
CT-04
Shays (R) 106,558 51
Farrell (D) 99,913 48
Maymin (L) 2,998 1
NJ-07
Ferguson (R) 95,830 49
Stender (D) 92,591 48
Abrams (I) 3,064 2
Young (L) 1,989 1
NV-03
Porter (R) 102,176 48
Hafen (D) 98,210 47
Hansen (I) 5,326 3
Silvestri (L) 5,155 2
WY-AL
Cubin (R) 93,336 48
Trauner (D) 92,324 48
Rankin (L) 7,481 4
The theocon and neocon takeover of the Republican Party has left many of its more Libertarian members adrift with few alternatives. I clearly hope the Democratic Party becomes more Libertarian friendly over the coming years, but that's a long-term project. In the meantime, the Libertarian ballot line (when available) can be an apt protest vote.
It can be argued that 58,000 Libertarian voters handed control of the Senate to Democrats, just as 97, 421 Greens in Florida in 2000 handed control of the White House to George Bush.
While Republicans try to fund Green candidates in races around the country, it looks like they have their own serious third party problem.