I'm posting prior to reading others' comments, so someone may have already said what hit me quite hard upon reading this.
The matter isn't just an antiseptic break with protocol. It's a serious breach and another one of the bona fide reasons why many voters recognize the whole process as tainted.
Americans are taught to love (and identify with) a winner! When it's drummed in day after day that Hillary has enough delegates to have clinched the nomination, she is anointed before her time and before DUE PROCESS actualizes a genuine outcome.
Still, a lot of people will hear the constant insistence that Hillary is the undisputed winner and rather than bear up to a baboon like Trump, they will vote for her.
If perception wasn't important, there would be no multi-billion dollar advertising and PR businesses; and the job of those entities is to manage perception. Again, a major component of the process is repeating a lie often and/or insisting that someone is a winner and anyone contesting that, reflexively, a loser. And many Americans have been conditioned to dislike losers.
A lot of conditioning is going on... plus the subliminal use of memes is very difficult to prove since their mouthpieces can argue, "That's not what I said." The nature of the subliminal message is that it isn't spelled out; yet its intent is known and felt all the same. That makes these artifices very potent, and experts in their usage know that quite well. Their 6-figure salaries depend upon that.