Jacob Levy, a political scientist at the University of Chicago, emails in response to the question about why third parties don’t run for congressional seats.
“This just isn’t true. No less than John J. Miller has written about all the Libertarian candidates for Senate who, arguably, have tipped at least three races to the Democrats in recent years (Washington, Nevada, SD, if I recall correctly). Libertarians contest most Senate races, and have made it a point in recent years to contest a majority of US House races as well. The other actual parties– Green, Constitution, etc, as opposed to one-man campaigns like Anderson 80, Perot 92/96, Nader 04– also run some downticket candidates. Typically a moderately credible third party Senate candidate will get more coverage, as a share of the race’s coverage, than will a third party presidential candidate. (The former might be let into debates, for one thing.) It’s just that that coverage is all pretty localized; there’s no national splash.
“At this point it’s not as though capturing 10 US House seats is a much smaller mountain to climb than capturing the Presidency. After all, Democrats might do the latter this year but have no chance of doing the former. Only a tiny number of US House seats are competitive.”