Wow, for all the talk of SEIU being so radical and saying that labor needs to do things differently... They're just doing the same-old, status-quo strategy.
Basically, they endorse the guy who gave a few small concessions, so that they'll get a few more. They'd also make the argument that if you don't endorse the incumbent who gave you a few small things, future leaders won't bother to make those small concessions because they won't be able to rely on labor rewarding them for doing so when the election comes up (which is a valid point).
But, still, this strategy really only helps guarantee that no real change is made.