I recently had a piece in the New York Times singing the praises of contested conventions. It being an op-ed, I didn't have the space to elaborate on some of the details. So I have been elaborating here.
The short version of the argument is this: A convention of unbound delegates would be a great way to choose a nominee. And we could get that, at least sometimes, if the parties used proportional representation and a shortened calendar. Then if we had a divided field, each would be represented at the convention in proportion to their popularity. But this would require taking delegate selection seriously.
Part III: Choosing delegates
If delegates are supposed to make the decision, we'd need good delegates. If you are planning for a contested convention, delegate selection matters more, because the delegates themselves would matter more.
But voters can't be expected to know much about individual local politicians — the sort of people who run as delegates. So they would run, as they generally do now, as affiliated with candidates. States differ on the technical details, but in a true proportional system, it might work like list PR does in most other democracies.
In list PR, each party has a list of candidates, and election officials go down that list until they have reached the right number of delegates. The parties, of course, choose candidates they believe will serve their party well.
For the nomination, each candidate would have a list of delegates who would be chosen because they would serve their candidate and their interests. Sanders would choose delegates who want to move the party to the left. Rand Paul would choose delegates who share his libertarian view of the Constitution. Ted Cruz would choose Tea Party delegates.
This might have several great side effects. It would encourage presidential hopefuls to develop good relationships with activists in many parts of the country. Politicians already need the support of local activists in state after state, but they don't need to get to know or trust them.
It also means being a delegate is more than just a perk for a politician. It requires those on the floor to be able to negotiate, bargain, and learn about the rest of the party. A party that needs those skills will cultivate and seek out those skills. Politicians who have had to bargain with those within their party may be better suited to bargaining with those across the aisle when, later in their careers, they win legislative office.
If we want robust parties, they need to be made up of politicians who are invested in them. Making the national party convention matter helps cement those investments.