It's a shame the Democratic party leaders did not understand sooner what their counterparts in the Republican party quietly accepted, enabled and in some case promoted. The party rank-and-file was much more ready and willing to accept the "radical" agenda that Sanders was promoting (as I suspect much of the American public is -- not enough -- but much).
With every ridiculous, racist, isolationist, or misogynistic statement Trump made, his popularity among people voting in the Republican primaries increased and his hold on the nomination strengthened. There is no way a candidate who said about John McCain what Trump did in past primary cycles would have survived. The party establishment would have spoken loudly about Trump's need to withdraw and would have made it clear that were he to remain in the race he would have the nomination stripped at the convention. But the party realized a huge swath of Republican voters not only tolerated what he was saying, they AGREED with it. So they let him be and quietly made it clear that were he to "earn" enough delegates, he would be their standard bearer come the conventions.
Had the Democratic Party establishment recognized Sanders' staying power early on he may very well have won the nomination. Had he received labor union support in Iowa he would have run away and hid with an Iowa caucus win. I know, I was on the ground there in the days and weeks leading up to his virtual tie. My colleagues and I talked with 1000s and 1000s of union members and the support for Clinton was tepid at best but the refrain was always she was mainstream and could win. They were itching for someone to support that they believed truly had their backs. But by encouraging establishment support and anointing Clinton as the de-facto winner, the party's normal allies never took a closer look and tried to ascertain where their support would have done their interests the most good.
I agree completely that the Sanders campaign made a difference in where Hillary will run on a number of issues this fall, but in my opinion the party would have been better off with the real thing. If the party possessed the proper foresight, running against someone like Trump should have been a dream come true. Yes, I am on record as saying that the country is full of brain-dead morons who have an orgasm every time Trump outdoes himself with some vile statement about Muslims or Mexicans, but I doubt it's more than half the electorate. A worthy opponent to Trump and we'd have likely seen an electoral college landslide that would have made Reagan, Nixon or LBJ jealous.
This election and my worries, some rational, some perhaps not, is actually starting to depress me.