Bernie Sanders is a "new flavor" for young people and Indies. Hillary wins big with DEMOCRATS.

What happened in MI, where Bernie won by 1.7 points in this open primary, was that Indies and young people who are responding to a BROAD and VAGUE message about the evils of Wall Street and an offer of free college tuition came out to vote in large numbers. Hillary won DEMOCRATS. Bernie is a new flavor and a lightening rod for anger and frustration at Washington and wanting big things that aren't going to appear anytime soon, like free tuition and Medicare for all. The Bernie supporters are motivated, and we have to give them that.

So what happened in MI was under-polled Indies and young people came out to vote and swayed it to Bernie by less than two points.
It is also very possible that some R's voted for Bernie, and some Hillary supporters stayed home thinking from polls that she was going to win easily.

What Hillary needs to do is to keep up the strong economic message and the message that she is the most prepared to beat The Trump and serve in the office of President. The jobs message is key. She needs to tout and explain her economic plan very well.