Of course, third parties have problems winning legislative seats as well, because unless they're able to negotiate for a position in the Democratic or Republican caucuses (after which, let's be honest, they are Democrats or Republicans anyway), they do not get committee assignments, and are soon sidelined and thrown out due to their ineffectiveness. They would really have to win a majority, or at least enough to deny any one party a majority, all in one stroke. That would take at least getting 30 percent of the vote in a house of representatives election; any less than that and, due to the nature of our system, gains rapidly fall away. A new party that isn't established in any specific region that gains, for instance, 20 percent of the vote nationwide, would likely win no seats at all. Parties like the Liberal Democrats are only able to survive specifically because they heavily target certain seats, and have a few traditional bases of support.