Top liberals call for Warren candidacy - They say that Hillary needs a Democratic opponent.

[Jim Lane]

44. I would love to see Warren as President, BUT...

The reality of modern Presidential campaigns is that you have to start very early. People like Bush, Cruz, O'Malley, and Sanders have been doing that work. At some point, "Warren hasn't done it yet" becomes "Warren didn't do it" simply through the passage of time.

We're not quite at that point yet. She could still decide to run, and if she does, I'll be on Act Blue later that day to send her a donation. Unfortunately, it seems likely that she'll continue to resist these efforts at a draft.

Even if she never runs, though, these demonstrations of support for Warren may be useful -- in influencing O'Malley. He has to decide on a strategy:
(1) Run a "nice" campaign in which he doesn't attack Clinton but just tries to demonstrate his own electoral strength. He positions himself as the logical choice to be her running mate if she wins, but if her campaign collapses then he's there to pick up the pieces and be the nominee.
(2) Run an unabashedly progressive campaign in which he tries to win over the Elizabeth Warren wing of the party, even if that means ticking off the Clinton camp and abandoning any hope of being VP.

My guess is that he was originally leaning toward (1), but the continued pro-Warren fervor may push him toward (2).