If Republicans have a rebuttal to Krugman, I'd like to read it. Claiming Democrats are just as bad, or that Krugman is an idiot does not count as a defense
Krugmans's claim that there are actions by Sanders supporters similar to what we have seen on the Right is correct. I have seen nasty comments from some who claim to be Sanders supporters. 
Krugman writes: "...we’re starting to see hints..." of a trend toward demagoguery on the Sanders side. But hints of a trend is hardly a long standing practice. Nor is it encouraged or even accepted by any but the most rabid Sanders supporters.
Each week a group of about 50 core Sanders supporters meet to discuss strategy and show encouragement. And each week the leaders remind the group that we should avoid personal attacks, asking "what would Bernie do?" The Bernie reference was demonstrated in his attempt to avoid personal attacks early on, exemplified by defense of the tireless attacks on Clinton's email. What candidate defends an opponent?