She did not steal an election from him. Sanders lost by MILLIONS of votes.
Yes..he lost by millions of votes, but it's quite clear that the party machinery worked in favor of Clinton and against Bernie. We have the very e-mails where they basically talk about how they're going to stop Bernie from stealing the nomination. Furthermore, the Republicans ran 19 candidates. The democrats ran 4. Is their talent cupboard so bare that they can't come up with 4 people (one of which isn't really part of the party) to run for president? No, clearly there would've been people who could've made a run who stayed out because the DNC made it clear it was Clinton's year to be coronated.
The media was also complicit. NPR, often declared to be too liberal, basically ignored Bernie or occasionally mentioned him as someone who was inconveniencing the inevitable Clinton victory. CNN has been called the Clinton News Network for decades. Even something simple like counting superdelegate counts in delegate totals was deceptive. If, say, they were reporting on a primary with 20% of the vote in, which Bernie was winning by 10%, they might list all the superdelegates in that state as part of Clinton's total, against Bernie's return from that 20% of the vote, and give the impression that Bernie was massively losing the primary even though he was winning.
Having said that...I still not sure Bernie could have beaten Trump. would he have been able to convince suburban moms to vote for him?. Would he have done even worse with Latinos and African Americans than Hillary did?. Would the Democratic donor class have gotten behind him with the force that they got behind Hillary?. Trump would have made up outrageous but entertaining lies about him and Republicans and some Independents would have believed every word. And he would have lost the Deplorables that won Trump the Midwest: they might like some of Bernie's policies, but to them he's still a liberal, an elitist, a jew, a communist, frail-looking for his age, who has spent virtually his entire life 'sucking at the public teat' (as the ads would certainly have put it).