The people saying Bernie can never beat Trump are the same ones who were saying Trump can never beat Hillary 4 yrs ago.
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I agree that no matter what, complacency cannot be an option on our side. HOWEVER, this is not the same thing. People who said Trump can’t win based it primarily on his personality and political inexperience. Saying Bernie can’t win is based on the fact that he’s a commie and the resulting policies.
It’s basic math. Right now, being conservative, Democrats and Republicans are essentially even in number. Voter enthusiasm for Trump within Republican voters, and a sizeable chunk of independents, are greater than we have ever seen (greater even than Democrat support for Obama). Turnout among Republicans will be extremely high, as it will for Trump-supporting independents.
What this means is that his Democratic opponent has two, very difficult, hurdles to overcome. One is to somehow lower pro-Trump turnout, especially in the new swing states in the upper midwest. But that hurdle is actually the easier one. The bigger problem is that a Democrat would have to, somehow, get Democratic turnout to rival Trump’s Republican turnout.
Sanders, quite simply, cannot do that. 20% of the party support him loudly and enthusiastically (and will have near 100% turnout - or as near as possible). Another 30-40% are at best lukewarm. He will win their vote, but their turnout cannot be expected to be anything higher than modest. And the remainder are adamantly opposed to Sanders. They will still vote for Sanders 9:1 (actually, it will be lower), but turnout there will be atrocious.
People don’t generally vote against their own self-interest. Obama was subtle enough, and people wanted to believe, so that people were convinced that a vote for Obama wouldn’t hurt them personally. This is not true for Sanders. He lacks any subtlety, and his entire platform is built around punitive taxation, wealth confiscation, and business strangulation.
Turnout for Sanders will be atrocious. For Trump it will be record breaking. Translation: landslide, with significant downticket implications.