It is true that a system built around precinct caucuses gives disproportionate influence to those who are motivated to show up and participate. But this is true of statewide caucuses as well. In Iowa, there are about 612,000 registered Republicans but only about 182,000 — or 29.7 percent — participated in the Iowa caucuses in February. No one calls that process illegitimate.
Trump also rails against what he calls “double-agent” delegates who, while committed to voting for him on the first ballot, may switch their allegiance on subsequent ballots. Well, if no one wins a majority on the first ballot, what are delegates supposed to do? Keep voting for the same candidate? If they did, the convention would be permanently deadlocked.
If Trump fails to wins a majority, then of course some delegates will have to switch their votes since the nominee must win a majority of delegates. Would Trump consider it unfair if Cruz or John Kasich delegates switched their allegiance to him on the second ballot in order to give him that majority? Of course not.