One line of defense against the Trump “rigged” charge is just to say that the rules are the rules. Jay Cost over at The Weekly Standard gets to a deeper point about why the rules make sense:
The Republican party does not belong to its presidential candidates in the way that Trump presumes. In important respects, it still belongs to the party regulars who attend these conventions. Starting in the 1970s, the party organization began sharing authority with voters to select the presidential nominee, but sovereignty was never handed over to the electorate lock, stock, and barrel. The delegates to the national convention, chosen mostly by these state and district conventions, have always retained a role—not only to act when the voters fail to reach a consensus, but to conduct regular party business.
This is hardly antidemocratic, by the way. Party organizations such as these are a vital, albeit overlooked part of our nation’s democratic machinery. The party regulars at the district, state, and national conventions do the quotidian work of holding the party together between elections: They establish its rules, arbitrate disputes, formulate platforms to present to the voters, and so on. It would be impossible to have a party without these sorts of people doing work the average voter doesn’t care about.
And these people are hardly the “establishment” in any meaningful sense of the word. Consider the process in Colorado. There was a hierarchy at play, no doubt—delegates at precinct caucuses voted for delegates to district and state conventions, who voted for delegates to the national convention. But the process was open to any registered Republican, and more than a thousand people served as delegates at the state convention. There were some big political players involved, naturally, but by and large they were just average people. The same goes for the state conventions in places like Wyoming and North Dakota. These meetings in Cheyenne and Bismarck are in no way beholden to, or the equivalent of, the power players working on K Street.
Trump might retort that Cleveland delegates should never be unbound from him, that they should be required to vote for him through the duration of the convention. But how would the party ever reach consensus in a scenario where no candidate won a majority and every delegate is bound forever? If the voters cannot agree among themselves, then somebody has to find the middle ground. The convention delegates, chosen through a fair and open process at the precinct, district, and state levels, are an obvious choice to complete this task. And this indeed will be their job in Cleveland.