A lot of people will, as part of the ongoing debate about how miserable and grinding the current election is, talk about how frustrating it is that in America we only have Trump and Clinton as viable options because "we live in a two-party system". (Usually, this is right before they talk about writing in Mickey Mouse, and right before I deliver a long and boring discussion of tactical voting that I'm going to skip this time out, which is kind of a shame because I have a great analogy but I'll save it for later.)
The problem is, this isn't untrue. We don't live in a two-party system. We live in a two-competent-party system. There's no reason encoded into our nation's laws that genuinely prevents a third party from forming, and in fact there are actually something like one hundred political parties currently operating in the United States. But most of them are content to run essentially as ego-stroking campaigns for their members, insisting that they would totally win if not for "bias" and "a rigged system" while ignoring their own clear issues that prevent them from gaining a foothold beyond the occasional Congressperson or state official. Here's why you don't see a national third party that competes with the Democrats and the Republicans, and why it has very little to do with media coverage or any rigging that might be going on.
1. Third parties don't put in the work. The Green Party runs a Presidential candidate every four years, and insists each time that their momentum is growing and that they're going to take back the mantle of "liberal" from the centrist Democrats. But a) nobody has ever explained how President Stein will get her agenda enacted when she has literally no Congressional support, and b) nobody has ever explained how a party with absolutely no track record in government will suddenly do a great job in that field.
The fact of the matter is, a third party needs to be built from the ground up, not the top down. A Presidential run is great press, but any third party that wants to have a hope in hell of enacting their agenda needs to have a full ticket--a Congressperson for every district at minimum, Senators for the 33-34 seats up each year, and probably local representation as well. But that kind of work is boring and low-profile, while running for President is exciting and fun and entails lots of interviews with people who really want to know your opinion! So the Green Party is Jill Stein every four years talking about how unfair it is that she never gets elected.
2. Third parties are fringe. Both the Libertarians and the Greens this year are presenting themselves as alternatives for those in the Republican and Democratic (respectively) Parties who want a candidate who's more true to their beliefs. Meaning more conservative for the Libertarians, and more liberal for the Greens.
The problem is, a candidate who trends toward the far end of the political spectrum is going to have less appeal to the middle, for obvious reasons. And if you have less appeal, you get fewer votes. A third party that gets fewer votes doesn't get elected. Once you start selecting for ideological purity and campaigning for the outliers, you're not going to win. Hell, that's the problem the Republicans have this year, which is why they nominated a sculpture of Mussolini made entirely out of pre-chewed Cheetos.
3. Third parties tend to be single issue parties. This isn't so much true of the Greens and the Libertarians, who are least are making a pretense of caring about actual governance, but something like the Alaskan Independence Party is basically running on the issue of, "Hey, seceding from the United States would solve all of Alaska's problems!" (I assume the "Rent Is Too Damn High Party" in New York state has a similar approach, but I'm not quite sure what their issue is. Probably legalization of marijuana or something.)
The problem is, this is a nonsensical approach to governance. There's no single fix that can be pushed through that will solve the problems the United States experiences on a yearly basis, and generally these candidates tend to be delusional people who have focused their emotional energy on demanding one unworkable fix because it's easier to believe that you can Solve All the Problems with one heroic swoop than it is to deal with the years of constant and unrewarding work needed to make the world a better place. Most people know this, which is why these parties tend to only attract a few true believers who are just as delusional as the candidate. Which brings us to...
4. Most third-party candidates tend to be delusional nutbags who build the party around their particular hobbyhorses, and they wind up more as cults of personality than viable attempts to do the work of governance. The obvious example that comes to mind is H. Ross Perot, whose stated goal was to create a pragmatic third party focused on practical solutions rather than ideology, but that wound up being held hostage to the narcissistic whims of its eccentric candidate. (Yes, I know, it does sound like the Republicans are rapidly descending into third-party status, doesn't it?) But really, I mean something like this guy:
Take a look at those proposals. This is a man sincerely running on a platform of disclosing the Pentagon's secret time travel program and admitting that we're already on Mars. This is the kind of thing that third parties in America are doing right now. They're not out there trying to become a viable alternative to the current two dominant parties, they're out there trying to put Bigfoot on the Endangered Species List. This is why we live in a two-party system. It's not because the Republicans and Democrats suppress the competition, it's because third parties are more interested in being symbolic forms of protest against an unpleasant reality than any kind of actual group interested in promoting responsible governance. Until someone--a lot of someones, really, because a political party isn't just something you make with your buddies in the garage--is willing to change that, a third party won't gain traction in America.
In fact, at this rate, we could be down to a "one-party system" in a few years unless the Republicans get their act together. But that's probably a separate post.