What makes you think it's been a crooked "in the tank" campaign? I voted for Sanders and am disappointed that he won't be the nominee, but the campaign looked fairly above-board to me.
I could see if there'd only been a few debates and forums, which might have looked like an attempt to keep anyone who didn't have name recognition at the start from competing. But there have already been nine debates and thirteen other candidate forums, none of which shut out Sanders.
It wasn't an ideal primary -- for example, ridiculously undemocratic caucuses continue to have an out-sized role, and the earliness of New Hampshire and Iowa favor candidates who are good at appealing to the (disproportionately white and rural) voters of those states. We can and should fix the process for future elections. I'd like to see open primaries in all states, with early states being more representative of the US as a whole (e.g., NY), or swing states (e.g., Ohio). But, even with there being room for improvement, it seems to have been a pretty honest and representative process.