Sarah Jones makes a good case that Bernie shouldn't run again, but ultimately her caveat ("But there's an important exception here. If there is no clear progressive frontrunner--no promising campaign for him to prop up--Sanders should run regardless of age.") has the most weight. It's just a sad fact that there is no progressive bench. Elizabeth Warren kinda sucks on everything except economics and she's given the impression that she doesn't want to run. Someone suggested Jeff Merkley but i think Sanders throwing his weight behind a relative unknown would have as much effect as, say, Sanders endorsing Keith Ellison during the DNC election. And the progressive movement getting behind another white male opens up the tedious identity vs. class "debate" all over again. Looking at Sanders' top surrogates, Tulsi Gabbard has taken some positions in the past that are problematic and i don't think Nina Turner has held high enough office to be a contender (i'd get behind her in a second, though).

If Sanders himself runs, i think he can win the primary by getting all of the progressive vote while the centrist vote is split between the Bookers and Cuomos or whoever. Unless Warren also runs, and i don't think Sanders will run if Warren runs (or vice versa). Yes, Sanders will be very old if he wins, but the model here is Ronald Reagan, who was personally doddering while in office but still managed to transform the political landscape for decades. Sanders (so far) seems sharper than Reagan and the important thing is all of the policies and appointments that he brings with him.