Does Sanders have the ruthlessness to win against an incumbent, a hostile party establishment, to remake the political order? This is what his supporters should be asking. As an outsider I do not have the same emotional connection to Bernie, but (to paraphrase Machiavelli) there’s an objectivity to outsiders commenting on politics. Is he too bound by custom and decorum to win what he wants to win? [Hell, no!] Leaving the declaration of victory on the table and the easy attack on his rivals, plus the DNC was not a good sign.
Perhaps Bernie and his supporters cannot win from the inside, but need to split and help build an independent left electoral force [no need for that to happen!] We Greens have been walking that path for decades. Sanders would give an independent left a jolt. Bernie would also have shown he has what it takes to defeat a system aligned against him for so long.