At what point is it fair to place the blame on the guy assembling the team?
It's always fair.
I think there are valid criticisms of Rizzo at this point. First and foremost is the ability to evaluate and develop pitching. We've always had problems in the bullpen. Rizzo made a great trade for Gio Gonazalez, but there have also been some serious mistakes. Rafeal Soriano, Jonathan Papelbon, Dan Harren, Anibal Sanchez, and Jeremy Hellickson (this season). We've already gotten a post on the bullpen, but I think that seeing how Treinen, Vasquez, AJ Cole, Trevor Gott, Craig Stammen, Yuemero Petit, and Shawn Kelley have gone on to have success speaks to a possible issue that needs to be addressed.