You read it here first, although it was very obvious: Jim Webb has an op-ed in today's Washington Post that says he is "in the process of deciding" whether to mount an independent campaign for President. Webb is certainly a different kind of Democrat, but the party is big enough to include him. He essentially failed to make his case in the debates.
In the op-ed he gives his rationale for considering a third-party run. What he doesn't do is paint a picture of how he could actually win.
Using Webb's campaign button in no way implies support or an endorsement. And to prove it, here: