I am harkening back to the 1984 Presidential election. Ronald Reagan was far ahead of Walter Mondale in the Polls. Then suddenly in order to boost his credibility Walter Mondale held a rally where 30,000 people showed up. It really looked awesome on TV. There was only one problem with that particular show. 30,000 people does not win anyone a Presidential election.
The moral of the story is that virtually any credible contender can summon at any given time and with reasonable organization a very large group of people as a strong show of support. But alas it is only just that, a "show".
Hillary will destroy old Bernie and go on to take the nomination (unless she is indicted then Biden will beat old Bernie).
As much as it pains me to say it Bernie Sanders will not move on to achieve the democratic nomination. Too bad, really, because if he did he would suffer the biggest defeat of any Presidential contender since Mondale was crushed by Reagan.
Ah..one can dream