Trumpkins frame a brokered convention in terms of the "establishment" denying Trump the nomination, or "stealing" it right out from under him. But that miscasts the issue.
i) To my knowledge, the rules for a brokered convention were drawn up before the primary season. They aren't designed to favor or disfavor any particular candidate.
ii) If Trump maintains his current pattern, where a majority of Republican voters oppose him, then he failed to win the key constituency. It's not the "establishment" taking something away from him. Rather, he failed to persuade even a majority of Republican voters. Since he's running as a Republican candidate, that's hardly an unreasonable bar.
iii) Indeed, Trump is staging a hostile takeover of the GOP. I wouldn't mind that if he were a solid charismatic conservative who could expand the base. But he's a Trojan Horse. There's no reason delegates should open the gates to the Vandals.
iv) As I understand the rules, it won't be party bosses in smoked filled rooms who award the nomination, but delegates.
There are two or three potential risks of a brokered convention:
i) It will alienate Trump voters. But from what I've read, these are mainly disaffected Democrats. They wouldn't normally vote for a GOP nominee anyway. So you're not losing voters.
And while it's nice to bring in new voters, there's evidence that Trump repels more voters than he attracts.
ii) There's the possibility that he will exact revenge by running as a third-party candidate. How damaging that would be depends on whether he'd pick off more voters from Hillary or the GOP nominee. He brags about his crossover appeal, but if so, that would drain Democrats from Hillary.
However, even if blocking Trump is politically risky, that's a necessary risk. This is a matter of principle. Sometimes the good guys are on the losing side. That's not a reason to switch sides and join the enemy.
iii) Apropos (i-ii), a brokered convention raises the specter of a televised brawl. A divisive event that signals dissension at a time we need to unify behind an opponent to Hillary.
However, that may well be a dated scenario. If it's clear that we're headed for a brokered convention, then it's likely that delegates will settle on a nominee in advance of the convention. In that event, the outcome will be a foregone conclusion–just as if it wasn't a brokered convention. As one pundit notes:
This year you can get delegate counts any time you want by going on RealClearPolitics.com, FiveThirtyEight.com or any number of other websites. You can bet that all the candidates have the cellphone numbers and email addresses of every delegate, and will be in touch (or are already) with those who are currently not committed to them but could, initially or on a second ballot, vote for them. They probably know which magazines they subscribe to and which websites they favor (hint: check them out on Facebook). Campaigns won't wait till July in Cleveland to get in touch. And when a campaign has enough commitments to get 1,237 votes, it will let the media know, even as the media try to figure out who's getting close.