Bernie Sanders inspired millions of young people to vote during the Democratic primary. Had he won the Democratic nomination, young people and more liberal-leaning Democrats and independents would have gone to the polls in record numbers on November 8th. If Clinton could win the popular vote against Trump, Sanders would have crushed Trump because of his huge and enthusiastic core of supporters.
Bernie Sanders had no chance to beat Donald Trump because, but for a small number of millennial leeches who want everything handed to them, more rational people knew better. Sanders' method is to buy votes by giving things away. Smart people know there is no free lunch. All his utopian promises require money. And he never explained how he would pay for his rainbow colored world.
Bernie was able to tap into some of the same anger and feelings of being marginalized that appealed to Trump voters but Bernie didn't have the same type of mainstream support that Trump was able to get from the GOP. Even if Trump is a political outsider, he's still a celebrity and much more in the public eye than Bernie, so he would have a wider fan base to start with.
Bernie Sanders did not appeal to a mainstream group of people, enough that would have allowed him to beat Donald Trump. Sanders ran his campaign on the very far left side of the left side. That does not work to win an election. Clinton was the democrats best chance, but even that was not enough to win the election.