Jon, neither your article here nor Sanders has mentioned the most important qualifier (and 'litmus test') for any candidate who claims to be a true and principled 'Progressive' --- which is, being totally committed to overturning EMPIRE!
Here's a brief comment as to who is a 'principled progressive' against Empire, which I placed as a comment on today's NYT regarding the Times' question of whether either candidate is fully progressive --- as Bernie could be if he fully stepped-up to igniting the Second American Revolution against Empire:
"A true progressive is against and will expose and confront Empire in all its cancerous forms of acting like a vicious and militarist "Empire abroad", and imposing economic tyranny on the 'subjects' it deludes and oppresses with "tyranny at home".
Or as the late great Jewish intellectual and anti-empire professor, Hannah Arendt, tried to warn the German people about devolving and slipping from democratic Republic into Empire in the 1930s, "Empire abroad entails tyranny at home".
Bernie has done a great job educating and alerting the American people (like Paine and Revere did) about the 'coming of Empire' in its oppressive economic tyranny "at home", but needs to recognize, publicly 'call out', and commit to non-violently confront the current 'foreign policy' (endorsed by Clinton) of our once proud country now "acting like a global Empire abroad" --- which even the trusted "Greatest Generation" author, Tom Brokaw implied on "Meet the Press" when he said, "When Trump and Cruz talk about refugees and 3 year old orphans, what we're really talking about is refugees and orphans caused by American foreign policy" --- which stuck me akin to the truth that Walter Cronkite spoke in his TV special report on the Vietnam War, and which caused LBJ to reportedly say, "If I've lost Cronkite, we've lost the war".
But Chuck Todd and the other so-called pundits at the round table sat mute after Brokaw's comment."