This falls under the category of good news-bad news because as a practical matter it gives Bernie Sanders more power to push the Democrats further to the left. Hillary Clinton needs to bring these voters in which means that she needs Bernie. And that means a deal will likely be cut. And once Bernie is on board, the numbers may change.
A June 14th Bloomberg Politics national poll of likely voters in November’s election found that barely half of those who favored Sanders — 55 percent — plan to vote for Clinton. Instead, 22 percent say they’ll vote for Trump, while 18 percent favor Libertarian Gary Johnson.
But it also highlights the peculiar situation in which the nominees of both parties are potentially expanding into formerly hostile territory while facing troubles with their core base.
Considering Hillary's numbers though, Democrats might decide that they don't need these voters. And that might be false confidence as polls tend to underreport Trump supporters. It might also convince Democrats that they can safely cast a protest vote without electing Trump when they really can't.