"That game was fixed! They were using a freaking ladder for God's sakes!" - Krusty the Klown
Whatever one thinks of the Associated Press's troll masterstroke of calling the nomination for Hillary Clinton the night before the final contests, it's been apparent for months that Clinton had staved off the insurgent challenge from Bernie Sanders. Strictly from a numbers point of view, the only time it looked like Sanders had a chance was after he massively outperformed his poll numbers in Michigan on March 8th. Had he repeated that feat a week later on March 15th, he had a shot. He couldn't and that was it.
Plenty of Sanders supporters cried foul both before and after that happened, and not without cause. The DNC was anything but majestically neutral, and since each state has its own homegrown arcana of a nominating process, there were always obscure rules and unfair quirks that could be shouted about on Twitter or on TV. (Hell, the Sanders and Clinton campaigns themselves were often baffled by some of this stuff.) But weird delegate allocation rules (in Iowa, Nevada, or anywhere else) didn't beat Sanders.
Sanders went down because Clinton cleared the field, and she didn't do it with any election night shenanigans in 2016. She did it House of Cards style, spending 2012-2015 working Democratic Party backrooms to keep anyone even remotely threatening to her 2016 bid on the sideline. It's easy to forget now, but for all the talk of the "deep bench" on the Republican side last year (which got quickly exposed as a collection of grifters and empty suits), the Democrats actually did have a deep bench that could've pushed Clinton harder than Sanders did.
The governor list is thin these days, but Team Blue has an embarrassment of riches in the Senate. Ron Wyden, Sherrod Brown, Kirsten Gillibrand, Tammy Baldwin (my personal favorite), and several others are excellent Presidential prospects on paper, and while a few of them garnered some press attention, none actually tossed in their hats.
Clinton's only competition from within her party was from one ex-senator and one ex-governor. That's astonishing and unprecedented. In a presidential election year with no incumbent (or even a VP incumbent), not a single sitting Democratic senator or governor sought the nomination. Nothing even remotely like it has happened since the nominating reforms of the 1960s-70s.
Instead of a thicket of candidates like 2008 or 2004, her only competition came from Sanders, who's even older than she is and wasn't a Democrat until last year. Preemptively clearing the field was her killing stroke, and she struck it before Bernie had so much as announced his campaign. The smoke filled room of yore has transformed into months of meetings in airy conference rooms, but the result is the same. Obscure and unrepresentative party officials and donors made the pick and presented her to their voters as a fait accompli.
There remained plenty of rank-and-file voters, both independents and Democrats, who didn't want Clinton, of course. Whether it's because of her Iraq vote, because she's a woman, or her coziness with the odious likes of Goldman Sachs, Henry Kissinger, and even Bush the Younger, there was no shortage of reasons to vote against her. She just made sure that the only alternative was old, white, and crotchety instead of young, black, and cool.
As with most things Sanders-Clinton, how you choose to perceive that is up to you. Was it a Machiavellian power grab that abrogated any real choice on the part of voters? Yes. Or was it a measure of how genuinely popular and respected Clinton is within the Democratic Party? Also yes. Either way, Bernie was doomed.
The questions the Democratic Party has to ask itself now are about whether or not it wants to keep its omnishambles of a nominating process more or less intact. Does it still want to privilege overwhelmingly white Iowa and New Hampshire? Does it still want to let each state come up with oddball rules that make the national party look foolish? Does it want to protect its prerogatives as a semi-private "party" when media technology makes previously obscure party machinery easily scrutinized by the masses?
These are not simple questions, and there are a lot of stakeholders who will want to pull one way or the other on them. But if the Democratic Party is going to rely on the votes and donations of the oft praised "coalition of the ascendent" for the next couple of decades, it might be a good idea to reform the system.
If they're going to allow a lone party stalwart to make herself the only option before ordinary people are allowed to cast even a single ballot, that's fine, but don't drag things out for five months doing it. And if they want to have a serious and fair contest that lets voters in more than just a handful of states have a meaningful say, that's probably better. But don't try to pretend that's what the current system does. Anyone claiming so looks silly.
Party nominating processes are not under any legal obligation to be small-d democratic, but in a time when it's becoming harder for a lot of Democratic constituencies to vote, further discouraging them from doing so by making the nomination a coronation is a plainly bad idea. The Blues aren't always going to have someone as buffoonish and incompetent as Donald Trump to run against.