One more on this today. In 1968, when the Democratic convention nominated Hubert Humphrey despite McCarthy's primary victories, riots ensued. That was why the parties adopted reforms to base nominations on primaries and caucuses.
Right now, the Stop Trump movement is looking for a way to recreate that. Trump hasn't lost his polling lead yet. A recent CNN poll puts him ahead of Rubio by 33 points. Based on the polling average at RealClearPolitics, that looks kind of like an outlier (just as the one showing a Cruz lead was), but let's be realistic here. If Trump's numbers don't go down, both nationwide and in the upcoming states, and the GOP looks for some way to block Trump from the nomination, Cleveland will see some unrest. As a professor at an institution in Cleveland, I don't want to see my city burn. After all, our river hasn't caught on fire in decades...
You don't stop Trump by rules-mongering the convention. Not unless your goal is to fracture the party.
Maybe that is the goal. Maybe the Romney faction of the party wants an excuse to break up and then reconstitute the party. If they try, though, it might be violent. It wasn't peaceful in 1968.