In every presidential election I've voted in (every one since 1992), I've had only one surefire prediction that holds up almost every time: Anything can happen, and damn near everything will happen.
It's usually a safe bet. Some races get so weird that I declare them races where anything can happen, and everything (no matter how implausible) will happen.
1992 was one such race, with Ross Perot becoming a credible candidate, dropping out mid-race, and dropping back in not too long afterwards.
2000 only mildly weird… until election day itself. Nothing like a looming constitutional crisis to spice up a dull election season.
2016 is already a weird one, and we haven't even gotten a single ballot cast yet, much less even arrived in the year 2016 itself!
It could be so weird that the likely Libertarian nominee could run as the "normal" candidate, as observed by Todd Seavey at Splice Today:
I mean, if the Republicans end up offering someone as odd as Trump or Carson, and the Democrats offer a criminal such as Clinton or a socialist such as Sanders... couldn’t Johnson plausibly just run as the non-weird candidate for whom America has been waiting?
Johnson, after all, is a successful, smart, and respected former two-term governor of New Mexico, elected and re-elected as a Republican even in a majority-Democrat state. He never raised taxes even when building new highways, shrank the budget, vetoed more legislation (from both parties) than any other governor, created more jobs than Rick Perry’s Texas despite occasional claims to the contrary, and let the state government workforce shrink through attrition as workers retired—probably the least-painful way to deal with public-sector bloat.