Are progressives shooting themselves in the foot?

In this clip a caller asks Nina Turner and Hartmann this question in a roundabout way. The caller talks of recent elections in Seattle, where two progressives ran and split the progressive vote so thoroughly that the establishment candidate won. He also asks about the upcoming Convergence Conference wherein a progressive coalition is forming and trying to get Bernie to run within a People's Party. Turner makes clear that Sanders, while critical of the establishment Dim Party, wants to still reform it. Turner, as head of Our Revolution, sees that as their mission as well.

That is the debate for the progressive soul. The Dim Party establishment is always trying to denounce the progressives as impractical purists, despite the progressive agenda being much more popular with the majority of people polled. So progressives may indeed get more stubbornly entrenched against the Party to the point of losing elections. And the Party itself just gets more entrenched against their progressive wing and indeed becomes even more center-right. But as we've seen, that almost always loses too. So maybe Bernie and Nina are right, in that we need to reform the Party?