Not that Hillary was going to be the nominee. Not that Obama was in her camp. But by the gratuitously insulting and imperious way in which Obama, on behalf of Hillary, shut Bernie down.
Bernie was not going to win the superdelegates. Obama could have worked with Hillary quietly, behind the scenes to ensure that, and to make sure the convention went smoothly enough, while maintaining his public neutrality.
By endorsing Hillary at this time, in this way--within minutes of his meeting with Sanders where Bernie had praised Obama for not "putting his thumb on the scale," before Bernie had even started his next meeting of the day, before the final primary, before the vote at the convention that formally decides the nominee, and with an ad that Obama had filmed for Hillary in advance, posted on Facebook by the Clinton campaign--Obama was making a deliberately excessive gesture.
He was effectively telling Bernie, in a publicly brutal way, who's the boss: "You've had your fun. Now get with the program. Oh, and, by the way, as you leave, make sure that those little 'uns you got all riled up vote for Hillary."
Forget thumb, Obama put his fist on the scale, effectively telling the superdelegates how he wants them to vote. Obama is now campaigning for Hillary while Bernie is still officially in the race, and daring Bernie or anybody to complain about it. "Hey Bernie: Not the superdelegates, not anybody in this party, is going to defy me. Are you?"
Bernie supporters should certainly be pissed off. But, again, this was predictable. It confirms a truth that Bernie (and most of his supporters) did not want to face: You can't run against Clinton without running against Obama. They are two head of the same Hydra. The neo-liberal and warmongering policies Bernie is attacking Hillary for are those of the Obama administration she was an integral part of. Obama is acting as the head of the Clintonite, counterrevolutionary organization that is the Democratic Party. Anybody who expected another result from running in the Democratic Party--or from Obama--hasn't been paying attention and/or has been engaged in wishful thinking.
If Hillary was going to win anyway, why did Obama make such a blatant exercise of power on behalf of the Democratic establishment? Well, Bernie's public torture on behalf of the ruling class duopoly is a nice enactment of the Foucauldian theater of punishment that's designed to demonstrate to the crowd that the sovereign can, precisely, do more than is needed to punish an errant subject. In immediate political terms, it's also designed to cut off, to forbid, any strong campaigning against Hillary on Bernie's part before and during the convention, which would necessarily involve further exposing serious dissension on substantive issues. Bernie was not going to get the delegate votes he needed, but Obama is now implicitly ordering him not even to try. "The Party and its supedelegates are mine (and Hillary's). Accept it."
And it's true: Hundreds of superdelegates will not defy Obama. Will Bernie? I think not, but we'll see right away. Bernie likes to say: "It's not about a man. It's about a movement." Now he has to decide whether it's about a Party or a movement. The choice for Bernie, which Obama has right now made clear, is to capitulate to the Democratic Party or to become a leader of a movement fighting for progressive change, independent and disruptive of the lesser-evil duopoly that pleases and perpetuates the ruling class.
For such a movement, the only thing left to do with the Democratic Party is to blow it up. The only reason for Bernie to continue his campaign and go to Philadelphia is to--in defiance of Obama, Clinton and the party establishment--press for public, irreversible positions on specific programs like single-payer healthcare, under threat of leaving with his supporters. Which he would end up having to do. The only reason for serious progressives to go to the Democratic convention is to demonstrate as militantly against the imperialist, neo-liberal Democratic Party as they do against the Republicans. To paraphrase Jill Stein: Most of what they're afraid Trump might do, Hillary, and Obama, already have.
If, after this gratuitous insult, this blatant attempt to shut him up and put him in his place, Bernie does not leave this rotten Party, many of his supporters will. In which case, Bernie will end up less the effective sheepdog than the pathetic sheep.