Don't throw away your vote on a major party -- vote 3rd party and mean something
It's common for people to write that those who vote for a minor party in an election are "throwing away" their vote. Here's a recent article by my friend Clay Shirky declaring there's no such thing as a protest vote and many of the cases are correct, but the core thesis is wrong. Instead, I will argue that outside the swing states, you are throwing away your vote if you vote for a major party candidate.
To be clear, if you are in one of the crucial swing states where the race is close -- and trust me, you know that from the billions of dollars of ad spend in your state, as well as from reading polls -- then you should vote for the least evil of the two party candidates as you judge it. And even in most of the country, (non-swing) you should continue to vote for those if you truly support them. But in a non-swing state, in this election in particular, you have an additional option and an additional power.
Consider here in California, which is very solidly for Clinton. Nate Silver rates it as 99.9% (or higher) to go for Clinton. A vote for Clinton or Trump here is wasted. It adds a miniscule proportion to their totals. Clinton will fetch around 8 million votes. You can do the un-noticed thing of making it 8 million and 1, and you'll bump her federally by an even tinier fraction. Your vote can make no difference to the result (you already know that) and nor will it be noticed in the totals. You're throwing it away, getting an insignificant benefit for its use.
Of course, the 3rd party candidates had no chance of winning California, or the USA. And while they like to talk a pretend bluster about that, they know that. You know that. Their voters know that. 3rd party voters aren't voting to help their candidate win, any more than Trump voters imagine their vote could help him win California, or Clinton voters imagine they could affect her assured victory.
Third party voters, however, will express their support for other idea in the final vote totals. If Jill Stein gets 50,000 votes in California, making it 50,001 doesn't make a huge difference, but it makes 160 times as much difference to her total than a Clinton vote does, or 100x what a Trump vote does. Gary Johnson is doing so well this year (polling about 8% of national popular vote) that his voters won't do quite as much to his total, but still many times more improvement than the major party votes. Clay argues that "nobody is receiving" the message of your vote for a third party, but the truth is, your vote for Clinton in California or Trump in Texas is a message that has even less chance of being received.
A big difference this year is that the press are paying attention to the minor parties. This year, you will see much more press on Johnson's and Stein's totals. It is true that in other years, the TV networks would often ignore those parties. In some case, TV network software is programmed to report only the top two results, and to make the percentages displayed add up to 100%. This is wrong of the networks, but I suspect there is less chance of it happening. Johnson will probably appear in those totals. Web sites and newspapers have generally reported the proper totals.
Does anybody look at these totals for minor candidates? Some don't, but the big constituency for them is others interested in minor parties. People want a tribe. Many people don't want to support something unless they see they are not alone, that others are supporting it. Johnson and Stein's poll numbers are already galvanizing many more votes for them.
This is how third parties arise, and it happens a lot outside the USA. In the USA it has't happened since the Republicans arose in the 1850s, tied to the collapse of the Whigs. Prior to that multiple parties were more common. Of course, there have been several runs at new parties (Perot/Reform, Dixiecrat and American Independent) which did not succeed. But if everybody refuses to actually vote for the 3rd parties they support because it is viewed as a waste, of course no 3rd parties will ever arise. Having a slim chance at that is one of the things to drive 3rd party voters, because that slim chance still means making a bigger difference than a meaningless extra vote for a major party.
This is how most political change happens. Because people see they are not alone. That's how small marches and protests grow into bigger ones until leaders are toppled. It's how small movements within big parties, and whole 3rd parties rise. As Clay recognizes, 3rd party votes have certainly "spoiled" the 2 party system, most recently in Florida 2000. Most Green/Nader voters there probably were not pleased with how they affected the election, but affect it they did.
What is the purpose of voting?
As far as I know, there has never been a tie or win by a single vote in a US state in the Presidential election. There have been ties in local elections, decided by cards or dice. But effectively, no one voter has ever made a difference, if your definition of difference is "altered the result." Never. In fact, one theory why voter turnout is so low is that many people believe their vote can't make a difference. And they are right, if they use this definition.
But if the purpose of your vote is "show the world that there is support for this idea" then every vote makes a tiny difference. It's just proportionately larger with minor candidates, and certainly not less in impact than a vote for major candidates. If we consider California, imagine that 100,000 extra people decide to vote for a minor candidate. It won't make a difference to Clinton's assured win. It will be barely noticed in Trumps or Clinton's national totals. But it would be massively major for the minors. It would bump Johnson 60% from last time, and more than double Stein within the state. People would take notice. They would notice in the major parties, and possibly adjust positions, but most of all the supporters of minor parties, who don't bother to vote for them because they don't feel it makes a difference -- they will see they are less alone, and be more likely to join the fight they really want.
You probably already know you are not in a swing state
You can decide to vote this way today. That's because you are in one of 3 classes of states. There are the core swing states, namely Florida, Pennsylvania, Ohio, Virginia, North Carolina, Colorado, Michigan, Minnesota, Iowa, Wisconsin, Nevada, Georgia, New Jersey and Arizona. You should vote major party here, though polls might push a few of these states out of their status. There are the "near" swing states which might come into play with some major shifts. If you look at polls you will know.
But if you are in one of the safe states, you don't need to track the polls. You know today your vote can't change the outcome of the election. That's because in a state like California, if things change so much so that Trump enough to Clinton that your vote might make a difference -- then Trump has already won outside California. So many other states would have to switch to him, including certainly all the swing states, that even if California is a tie, your vote won't change who becomes President. (It could change the size of the Trump landslide, so it will make a difference, but not in who becomes President.)
But these guys are crazy!
Many people will say they would not vote for a 3rd party because their platforms are much too extreme, and their candidates often clearly unfit to be elected. But this presumes you imagine they might win. They are not going to win. Who the candidate is means little. They are a symbol for their party, which means a symbol for a few of its core ideas. The Libertarian party wants a vast reduction in the size of government, and less government interference in our personal lives. That's all you need to know about them. You don't need to know where Gary Johnson stands on the department of education. His personal stances are largely irrelevant. Stein and the Greens stand for a progressive, pro-environment agenda, and that's all you care about there. That she thinks wifi boxes might harm our children is irrelevant. If either of these parties become bigger, they will field new and better candidates, and also moderate their positions.
It can make sense to vote for a minor party even if you actually prefer the platform of a major party. The major party actually might implement their platform, so you should read it. By supporting a minor party, you may not ever bring it to power, but you will cause other parties to adjust their positions (or sadly, sometimes just their messages) to reflect the demonstrated body of voters who feel that position strongly enough to vote that way. (It should be noted that this can also be done by becoming active within a major party and trying to push it in your direction. The Tea Party movement is an example of the success of that, as is Trump.) I do believe that a strong Green showing would move the Democrats a little in that direction. Even if the Tea Party or Sanders approaches might do that more strongly, it is wrong to say the rise of the 3rd party is completely ineffective. It clearly is in other places around the world.
I will point out that there is an exception to what I have said above. If you think the 3rd party is controlled by is candidate, and that candidate is truly evil and would continue to control it as it rises, then you probably want to stay away. The negative example from history is fairly obvious here. (I find it bizarre, in fact, that Hitler was actually a German Army Intelligence officer sent to infiltrate and spy on the new rising German Worker's Party, and he did such a good job of infiltrating it that he ended up taking it over and made it his personal cult. One wishes his commander had assigned him something else to do.)
What about vote trading?
In the 2000 election, many people proposed vote trading. There, in sites like "Nader Trader" they would pair up people in swing states who wanted to vote Nader with people in safe states who wanted to vote Gore. They would agree to swap, making sure Gore got support in the swing state and Nader's national total (which is what matters most) was maintained. Some of these sites were shut down as violating election law -- the eventual court case ruled that they were actually legal -- but they never had much success. For one thing, they required very engaged voters willing to be very trusting of a stranger. (After all, the other voter might ignore the deal and hope they were getting 2 votes for their guy, with the Nader voter having the strongest motive to do that.)
One could imagine doing this better today with mail-in ballots. Mail-in ballots should be considered an abomination, because they have eliminated the important principle of the secret ballot. But having done so, it becomes possible to verify your vote to a 3rd party. The simplest way to do that is to show your ballot to a 3rd party, seal it and sign it, and then drop it in the mail or give it to them to mail. As long are you are not compensated for this (except with another vote, which does not have monetary value) it should be legal. One could also imagine drawing your President line in a special ink (that you are given) which clearly can be seen when examining the ballot using a bright light of a certain colour. In that case it could all be centralized. You mail your ballots to the trusted auditors, they pair them up and put them in the mail, and they simply publish the current counts so you know the trade worked. (Ballots that did not get a match could be returned to voters who could then take them to ask for a replacement.)
This would be useful this year, but it does require a fair bit of action by the voters. I suspect funding for the independent auditors would be easy to find from both sides, as the trades are win-win.
The actual right answer
Of course, the right answer is multi-candidate voting, where you can vote for more than one, and sometimes express an ordering. This is done in Australia and several other jurisdictions, and is quite popular in private elections. With this, you can freely support minor candidates with no fear of hurting the chances of your preferred major candidate. My two favourite forms are Cordorcet and Approval. Approval does not collect your ordering of the candidates, which some would view as throwing away information, but its pure simplicity is a great virtue when you need the public to understand how the voting system they are using works. In preferential systems like Cordorcet, the advantage is there is no "strategy" to apply -- you always express the truth that you really feel in your ballot. In Approval, there can be some use of strategy (ie. leaving a choice off your ballot even though you like it to avoid it outcompeting your top choice.) But that simplicity is appealing.
States are, I believe, free to adopt whatever ballot system they want for their local elections, and the election of the Electoral College, which is what the Presidential vote actually is. Florida could adopt Approval if it wanted, and there would have been no risk of the 2000 debacle if they had.
The third parties could do a better job of it...
The minor parties in the USA are strange birds, though. While they all know intellectually that they can't win in the near term, they don't like admitting it, even to themselves sometimes. They go through the rituals of the major parties, holding conventions, declaring platforms, and selecting nominees based on their personal attributes, policies and character. Most of this is ridiculous and even harmful to the parties.
My advice to these parties would be to choose 1 or 2 core issues and make them their only issues. Aside from making their message simple to outsiders, this would greatly increase their membership and their votes. I often run into people who say, "I like the general idea of X, but I could never support a party that says Y." Small parties should stay simple, and then have more nuanced platforms when they get large enough to actually matter. Of course, this means the future, larger party will not stay true to the ideals of the core membership, because it will have more members and the platform has to please them. This is not tolerable to some.
As for nominees, they are useful as a spokesperson. You want somebody who believes the core message of course, but who can also subjugate themselves to it, and be a spokesperson for it rather than a leader. Being famous -- even hollywood famous -- is a good idea. And yes, they should say, "No, we aren't big enough to win this election, but we might win some local elections and we want the world to know there are many supporters of our message."
For the Libertarian party, I would distill their platform to one tiny fraction of it: "Repeal the marijuana prohibition." This is already a major plank of their platform, but more to the point, this now has the support of the majority. Many people would vote for that. Not so many that the party would win, but enough that other parties would add it to their platform. Then pick another issue. For the Greens, I would pick an issue like carbon cap and trade, or some other popular issue they are strong on.