Every now and then, in online player vs. player combat, we will see an extremely talented "other" player appear, break ranks, and trash both teams. He--stereotypically a he--will cause confusion, death, loss of objectives, and swearing--lots of swearing. And he is called a "spoiler" for spoiling the game.
     In political party vs. party combat, we will see an extremely talented thespian appear, break ranks, and get on TV. He--or she--will cause confusion, loss of objectives, poll changes, and swearing--behind closed doors. When this person takes election-day percentage from the parties, that person will also be called a spoiler.
     No matter who that person is in public--hero, savior, "a regular Audie Murphy"--that person is a stranger in congress--or will be. Like his online counterpart, the fact that this person has no party to follow means that he has no one to call on for favors. Without that, they can't count on votes, push agendas, sit on important committees. No matter the support in public, therefore, the person without a party is a person alone in congress. This also means that their "getting things done" rate is likely low.
     Therein lies the rub: without a party, the third-party congressperson is ineffective, and a feckless or would-be feckless congressperson is (likely) vote-less soon enough. In a republic (which this is), voters will put up with a lot to keep effective congresspeople working for them--which is why Strom Thurmond, Ted Kennedy, and a handful of others died in office--despite reprehensible events in their past (which I won't recall), these people had influence.
     I would argue that this is unlikely to change. The two parties have all the best seats in all four branches of government (Media, Executive, Judicial, Legislative), and the barriers to entry to all at once are quite high.
     Yet, the extra-party people serve a purpose. Their presence is as necessary as it is controversial, because as long as they exist, the center cannot be ignored. The problem with two-party republics is that there will always be some unclaimed, half-and-half, cannot-decide voters that subscribe to neither party fully. Putting aside the voter apathy problem, these people are usually asked to put aside differences of their own and "just pick one," usually egged on by "what one party doesn't believe, the other one does!" Horse-hockey. The two parties don't have all the answers, and the middle knows that. Off-party candidates DO have the answers--they exist for it--and their popularity causes the parties to re-focus. It is easy--extremely easy--for a party to energize its base, bray loudly about cultural issues and ignore the center, but it isn't until the center starts offering its own candidates to "spoil" that the hard work--re-gaining the center--gets done.
     Thank you for reading.