What’s the probability of a contested convention within the next 50 years?

[Mr. Morden]

What’s the probability that either major party will have a contested convention within the next 50 years?  I’ll define “contested convention” as there being genuine uncertainty going into the convention as to who will win the nomination and/or the nomination goes to a second ballot.

[LLR]

It's happened in the past 50 years, I don't see why it shouldn't happen again.

I think there will be another 1976 scenario, but maybe not a multi-ballot convention.

[beaver2.0]

Probably will happen.

[Mister Mets]

It'll likely happen at some point (90% chance, I guess). Divides within parties increase the chances of someone not getting a majority of the delegates, and we can expect 20 or so contested primaries in the next fifty years.

[Mr. Morden]

I really used to think that a contested convention happening in my lifetime was a longshot, since I figured the party elites would pull out all the stops to prevent such a train wreck.  But seeing how the 2016 primaries played out, it's become more clear that 1) the party elites don't have as much power as I thought, and 2) many of them would welcome a contested convention if it would prevent the nomination of someone who (in their opinion) is a terrible candidate.

There's also the fact that we could see delegate allocation rules change for both parties several times over the next few decades, and certain sets of rules are more amenable to a contested convention.  If the Republicans used the same proportional allocation rules that the Dems use, then a contested convention would have been a certainty this year.

[IceSpear]

It would be MUCH more likely on the Dem side, due to the proportional rules (as Morden mentioned) and the fact that GOP voters seem much more likely to rally around the frontrunner than Democrats do (At least lately. 2008 and 2016 have been demographic battles of attrition. They rallied extremely quickly in 2000/2004.)

We might have gotten one in 2008 if Edwards stayed in to be a kingmaker.

[Mr. Morden]

It would be MUCH more likely on the Dem side, due to the proportional rules (as Morden mentioned)

Under current rules, yes.  But the rules for both parties could change.  For example, if Trump loses really badly in November, then the Republicans may well change their rules to something more proportional, which would increase the chances of a contested convention, so as to decrease the chances of a Trump-like candidate winning the nomination in the future.