The RealClearPolitics average from May 6-June 5 had Sanders at 49.7% to Trump’s 39.3%, a 10.4-point cushion.
In that same time frame, Trump was polling close to Clinton and was even ahead in multiple polls.
During an appearance on Meet The Press at the end of May, Sanders acknowledged that disparity: “Right now, in every major poll, national poll and statewide poll done in the last month, six weeks, we are defeating Trump often by big numbers, and always at a larger margin than secretary Clinton is.”
That polling was of course based on a hypothetical scenario, five months from Election Day. However, Sanders’ popularity among white working-class voters might have been the difference in this election; voters that Trump ultimately won.