I already commented on this issue, but here's another aspect. Clinton's choice of Kaine, if she were truly serious about trying to reconcile the divisions in the party, was a huge mistake. And the reason can be summed up in three words: TPP. This is not a minor issue. The TPP is far worse than NAFTA, and is a deal killer for a lot of working people. And Kaine is a big supporter. Clinton claims to have decided not to support it "in its current form," but this VP choice is going to be seen by a lot of Progressives as a signal that she only said that to get votes, and that in fact she intends to allow this huge corporate giveaway to go through. You should realize that the TPP actually has next to NOTHING to do with free trade (we already have virtually tariff free trade with nearly all the signatories); and EVERYTHING to do with corporate control and deregulation of international standards (especially environmental standards) for the benefit of large business. (See
http://www.citizen.org/tradewatch for more information).
I see TPP as the single worst policy position taken by Obama in 8 years, and this just confirms that Clinton intends no change in this area. And here's the thing: these are "mainstream" REPUBLICAN positions. No daylight between them. But while he's probably lying about it, TRUMP says he's against it, and a lot of people will believe him. If Clinton's at all worried about people on the left of her party just not voting in this election (most will not vote for Trump, of course), she could hardly have made a worse choice.
(I am not one of them; I will of course vote for her, because the stakes are so high. But some will NOT.)