I'd love to!
So there's this thing called the Establishment, and they are the people who have been pulling the levers of power for a long time. They're the donors, the lobbyists, the think tank employees and, of course, the elected officials and their aides. Some of them are awful, some are probably great, but the vast majority are normal people doing their jobs. These are people who individually do not have much power, but are part of an extremely powerful system.
The average voter, however, does not see these Washington insiders as people they can relate to, and with good reason. Unfortunately, this does lead to an impression that there's a lot of nefarious shenanigans behind every single policy mistake when usually it's just incompetence, ignorance and human error. Which is equally damaging, but the correct response to a conspiracy is vastly different from the correct response to incompetence. The news media adds to this narrative and the result has been a large-scale break down of trust between the government, the public and even the media itself.
Remember, a healthy democracy needs all three of those groups in order to function--especially since the media is the main way in our current system that the public and the government can interact. That's bad enough, if only for the reason that media coverage distorts a message, but it's made even worse by the fact that the news media has stopped viewing itself as a public service and started viewing itself as a commercial enterprise. The stories that sell are not always the important stories that need to be told, and news organizations fill empty on-air hours with pundits who scream at each other over meaningless arguments which never go anywhere which further contributes to the break down of the three-way social contract based on trust that once existed between the government, the public and the media.
On the GOP side of things, the Establishment has been employing an effective tactic for the last few years--they've been branding themselves as the Just Like You Man On The Street Party. They talk about the out-of-touch establishment and the Washington elite, and many of their voters are attracted to that narrative. Now, when the insiders said these things they were not including themselves in the Establishment, but rather using "Establishment" as a dog whistle for "Democrat." The only problem being, they definitely ARE Establishment (think Cruz-who may be nearly universally despised but has still been working in the highest levels of government since the 1990s). But there were never any viable alternatives in campaigns, so before now this tactic never got used against them.
Only, this time, there actually IS an outsider candidate going up against the Establishment and all those years the Washington insiders spent convincing their voters that the Establishment was out to get them is coming back to haunt them. The Establishment does
not want Trump to get the nomination, mostly because they don't think he can win in November, but some of them because they object to him on moral grounds. The way they see it, he crashed their party and he's stealing the people who in previous elections voted for whoever the Establishment chose as their favorite. The GOP Establishment does not understand why people are voting for Trump.
What takes this into the level of revolution is the fact that many members of the GOP Establishment risk political backlash in their own districts just for being associated with the Republican Party if Trump is the nominee. That also helps explain why they're trying so hard to stop him through the delegate system, because a lot of Congressmen and Senators are terrified that if Trump is on the ticket in November it will hurt down-ballot candidates--the people running for the Congress, Senate and state governments that are also put on the November ballot. They're worried that if Trump is the nominee they'll lose their Republican majority in the Senate and maybe even in the Congress.
The Republican voters are voting AGAINST the Establishment, against the will of the Establishment and in defiance of every effort they have made and despite every resource at their disposal.
My theory is that, by spending so many years hinting that the Washington elite were actively working against ordinary people, the GOP has created a populist movement with a deep mistrust and even loathing of all authority figures (which in American politics is basically just the government and the media) and that the Republicans are just now discovering that they cannot control what they have unleashed. And what they have unleashed is voting for Donald Trump.