On the negative side for Sanders aficionados the short answer is it is almost beyond the realm of possibility. On the positive side a Sanders candidacy would do much better than Mondale's and McGovern's disasters.
Although on first glance the 2012 win by President Obama seems substantial it turned on the usual suspects, a small number of key states. If Florida/Ohio/Virginia/Colorado had gone to Romney. All within the realms of possibility as the margins commenced at 0.5% Romney would have been elected.
What gave Obama the victory was the unprecedented turnout of Black voters in Ohio without which state no Republican has ever won the presidency.
For Sanders, who is clearly struggling with Black voters at present, to gain the same amount of Black turnout in 2016 seems improbable. Thus the smallest decline in Black turnout (not to mention vote switching to Donald Trump should he be the nominee) would make his candidacy a struggle at the very least.
Worse, should Trump be the nominee and his prediction in his message of "bring back jobs from China" and Hispanics will support me because of jobs" that he would win the "rust belt states" of Ohio/Pennsylvania/Michigan come true, then Sanders would be finished.
A possible day after the 2016 presidential election would look like this in a Trump/Sanders match-up;
If Trump were not the Republican nominee, and Michigan and Pennsylvania went for Sanders the GOP would still win comfortably.
Perhaps surprisingly even if Ohio were removed from the GOP even without Trump as the candidate the Republicans would still win the presidency as the result would be a tie with the GOP dominated House of Representatives choosing the president.
