After the coordinated schemes to undermine him by the Hillary Clinton campaign, Bernie Sanders does not have very long to last in this election. All the odds are stacked against him, and it is already decided, but any more loses will finalize his defeat. The media, the establishment, and the DNC will not allow Bernie to win.
I don't think we should count Bernie Sanders out just yet. It has NOT been decided as to who will be the Democratic nominee, and especially if the allegations against Hillary Clinton continue, the DNC should take a hard look as to who they will want to put their support behind. It's not over 'til it's over.
The loss in the Washington D.C. primary was the final nail in the coffin for Bernie Sanders. The final nail was the large loss in California. Sanders was hoping for a big win there that he was hoping would compel superdelegates to vote for him at the convention. His loss there essentially ended his campaign.
No, the DC primary is not the nail in the coffin for Bernie Sanders. Sanders never had a real chance at winning the Democratic Party's nomination for president. Hillary Clinton was always the favorite among her party's establishment. The nail in the coffin for Bernie Sanders was his lack of support among non-while voters. Hillary was able to clobber him in heavily diverse voting blocks; giving her enough pledged delegates to win the nomination.