Clinton ran as a moderate. She promised to do some liberal things, but ultimately not to turn America communist or socialist. On the conservative side, when the Republicans run true conservatives, like Bush or Trump, they win. When they run moderates, they think it's going to be better, but they lose, like Romney did. Sanders would have done better than Clinton because he stood for more of what the democratic party really believes in.
When you compare the numbers of the last three presidential elections, you see that the Republican turnout has remained consistent, and even declined slightly. So how did the republican candidate win? Because the Democrat voters -- mainly the people who had supported Bernie Sanders and wouldn't support Hillary Clinton -- stayed home. Their turnout was about half what it was in 2008, when Obama was first elected. If Bernie Sanders had been on the ballot, those voters would have shown up to support their party and Sanders would have won.
Bernie's proposals would have cost trillions of Dollars, with no rational way to pay for them. He's already 75 years old. Bernie's wife was President of Burlington College, where she foolishly took on insane amounts of debt, and ran the school into the ground. It closed in May of this year. Bernie is too much of a kooky Socialist, with all the vulnerabilities therein.
Add it all up, and Trump would have won.
Bernie has a sold fan base, and they may have tanked the election for the rest of us. However Trump, although a political outsider, was a financial and social insider. He had connections, money and fame, so already reached a much wider audience than Bernie did or could. Even if parts of the GOP held their noses and voted, I don't see the Dems doing the same for Bernie.
There is no way on earth that Bernie Sanders could have beaten Donald Trump. What the selection proved was that not even Hillary Clinton, Who is about leftist, could come close to beating Donald Trump. How can one conclude that a Marxist like Bernie Sanders could have beaten Trump? What is clear is left-wing ideology was rejected in this election.