Bernie and the Democratic party
There is still time to nominate Bernie. The US Virgin Islands, Puerto Rico, California, NJ, Montana, NM, SD, ND, and Washington DC have yet to hold their primaries. Bernie would need a commanding lead in them to catch Hillary, but the possibility is there. Bernie knows what his tracking polls look like, more importantly, he knows what his phone bank results look like. The Bernie phone bank is tied directly into his database, so he knows how many calls are being made, where those calls are going, and what the results look like, and his team knows this in real time. But the biggest indicator that Bernie still has a chance to win are all the calls for him to withdraw. If he really had no chance no one would bother.
Versailles is very very nervous: How Senate Democrats are trying to deal with Sanders
Let's be clear, this is not about winning in 2016. In 2006 Lieberman lost the Democratic nomination and went on to beat the Democratic nominee. No one batted an eye, the donor community loved Lieberman, so who cares about the voters? Even after Lieberman endorsed John McCain at the 2008 Republican National Convention, no action was taken against him, nor were any public criticisms made. The Democrats could care less about party unity. They fear the base. Bernie has showed a candidate does not need the donor community, that you can defy the kleptocracy, and that is scaring the pants off them.