i think the first thing that leftists/progressives need to do is start asking hillary some questions. if she wants to represent the left, she's going to have to start explaining how she reflects ideas on the left.
so, what you need to do is start asking questions every time you see her. questions like this:
"when do you plan to table legislation for single-payer health care?"
well, she wants to represent the left. she wants bernie supporters to vote for her. she wants unity. obviously, then, she must have plans to introduce single-payer, right?
here's another one:
"given that you don't support taxes on wall street, how do you expect to fund an opening of tuition at public universities and colleges?"
again: she says she wants bernie supporters to vote for her. so, surely she has thought through how she plans to pay for this.
this one is really key.
"can you elaborate on your plans to withdraw american forces from the middle east?"
i think you get the point.
there's two components of this.
yes, there's a bit of sarcasm, here.
but, the truth is that you're going to have to do this. even if you end up voting for jill stein in the end. you should not give her a free pass, or give up, or drop these ideas. and, this is a kind of a non-confrontational way to demonstrate that there are real differences that can at best be glossed over.
if you just let her loose, she's going to immediately bolt back to the center-right, where she's most comfortable. so, you have to keep constant pressure on her to hold to whatever concessions you can get out of her - and constantly be pushing for more.
in the end, if she decides she wants to run on the right, you should force her to broadcast it. and, you should force her to deal with the consequences of it.
you fought too hard to just give up.