Anti-voting and third-party socialists, your argument has always been that it's impossible for socialists to compete in the two-party system. Until this year, I've agreed with you, but now the US is finally testing that theory. If Sanders fails, you will win new converts—see Poll: 33% of Sanders Supporters Wouldn't Vote for Clinton: "A new Wall Street Journal/NBC News poll indicates one third of Vermont Senator Bernie Sanders' supporters cannot see themselves voting for Hillary Clinton in November."
But a surprising number of them will go to Trump because they see him as the only other politician who cares about the working class—see The Bernie Sanders voters who would choose Trump over Clinton | US news | The Guardian: "In an NBC News/Wall Street Journal survey conducted by Hart Research Associates this month, 7% of Sanders voters said they could see themselves supporting Trump."
Backing Sanders now will make you more visible to his fans who wouldn't vote for Clinton. And if you manage to make Sanders do even better at the moment when the Democratic leadership betrays him, the betrayal will be magnified, and even more people will see the hypocrisy of the capitalist pseudo-left.
What's the worst that could happen? If he actually wins with your help, the working class ends up with a $15 minimum wage, free public higher education, and a President who is less hawklike than any of the other viable contenders. None of that stops you from continuing to fight the good fight.
Previously: The socialist case for supporting Bernie Sanders