I never though that i would be praising an article from TNR. However, this pieceby Michael Kazin makes a lot of sense.
Kazin starts out by noting that Bernie has been making a number of appearances in places like Iowa and has been making statements strongly suggesting that he is prepared to run for president. Kazin assumes, like most of Bernie's admirers, that if he runs, he will probably run for the Democratic primary and not do a Nader.
More below the orange puff of smoke.
Kazin believes that Bernie entering the race would be a good thing, even though he thinks it highly unlikely that the Senator would actually win. He points out that giving Bernie a national podium would help remind people which party gave them all those popular programs like Social Security and Medicare and would make independents and even some Republicans give the Dems a second look. In addition, if Sen. Sanders actually won or came close to winning a few primaries, he would embolden the likely Democratic presidential nominee, Hillary Clinton, and other middle-of-the-road Dems to follow an more left populist agenda.
Finally, Kazin makes the point that a Sanders candidacy would serve to excite the young voters and other progressives and assure the Democrats of a very friendly electorate in 2016.
I strongly suggest you follow the link to the article. It's not long and it's great reading.