Remember, we're not saying it will definitely happen. We're not even saying it might happen. But while we can, we can fantasize about a contested (not a brokered) convention, where no one is even close to winning a majority:
What happens then? Remember, the conventions are essentially the governing body of the political party. They have rules, but if they choose to change those rules there’s really no one (not the Republican National Committee, not the courts) who is going to prevent them from doing so. The majority of the convention, ultimately, is responsible only to itself.
Back when we had real conventions, one of the ways that nominations were fought out was over credentials. Rival groups would claim that they were the “real” delegation from one state or another. Ultimately, the convention itself decides. Anyone who recalls the extended dust-up over the Florida and Michigan delegations to the Democratic National Convention, a bitter fight that went on even after there was nothing at stake, can imagine how vicious something like that can be when the nomination is at stake. Given the various penalties that have been assigned as well as the dicey counting so far in the caucus states, there’s plenty of material available for some awesome, and awesomely ugly, credentials challenges.
For those of us who went through Florida and Michigan, it was fun, but Bernstein is right: "there was nothing at stake". Face it, if the nomination is really at stake, we're going to see the biggest political theater since, dare we say it, Chicago in '68.