from 1878 to 1950 there was always 1 member of a 3rd party in the United States House of Representatives, from 1950 to today no member of a 3rd party has been elected to the House.
what happen?
what happen?
The OP misses out on the phenomenon of independent candidates: take Bernie Sanders, Senator from Vermont and previously Representative from Vermont since 1991. While he caucuses as a Democrat and though he considers himself a socialist, he runs as an independent. And there's Joe Lieberman, elected in 2006 as an independent against a strong Democratic opponent. 2 out of 100 in the US Senate is quite a lot, particularly when one considers the power one senator can wield.
Furthermore, Minnesota has the Democratic-Farmer-Labor party: on the one hand one can dismiss it as the Minnesota State Democratic party, on the other, though, it has a distinctive history and ethos from the DNC. Indeed, at the state and local level, the US has several third parties that play some sort of role.
The years since 1950 have seen there share of third party / independent candidates: George Wallace in 1968, for example, as well as Ross Perot in 1992, to say nothing of Ralph Nader in 2000.