Bernie Sanders for the well-intentioned,
Those of us who have followed politics for years know that third party and write-in candidates typically split the votes for whichever of the other two candidates is closest. In Bernie's case he's currently running for the Democrat nomination, but a real threat will be if he fails and decides to launch a third party campaign for president in 2016, instead of throwing his support behind the presumptive winner (Hillary).
As a third party candidate (assuming his numbers continue to climb) he would more likely split the Democrat ticket, in effect tossing the election for the GOP. If my presumptions are accurate, anyone voting for Bernie in the general election would not see much difference between the other two main party candidates. In other words, there wouldn't be enough daylight separating them to make any difference which of them won -- so voting for the long shot would be better than not voting at all.
I hate to admit it, but when I think about it -- I'm getting there...
Those of us from Georgia remember well how Lester Maddox became our governor. He was not elected by an electoral majority, but by the Democrat-controlled Georgia legislature, in accordance with the Georgia constitution which stipulated that in the event no candidate got a majority there would not be a run-off, but the election would be decided by the legislature. And since Lester was the official Democrat and Ellis Arnall was the popular third party candidate, a write-in who failed to receive the necessary majority, the outcome was fait accompli.
I was out of the country at the time and didn't bother to send an absentee ballot. (I actually used it instead to show my Korean high school students how Americans could still vote by mail, even though not able to vote in person. They were quite impressed, never having thought about such a thing before. My absentee ballot was better used as a visual aid for teaching anyway.) A friend who was voting at the time said the alternative was between a sophisticated bigot and an unsophisticated bigot anyway. A vote for Arnall was a long shot, but Bo Callaway, the Republican and former Congressman, had been so negative in his former job he was nicknamed "No" Callaway.
If the 2016 presidential election is between Hillary and Jeb, I will need a lot more energy to be more than a lackadaisical Democrat, especially if Bernie is also on the ticket.