It is fairly clear that Roberts didn't make the decision regarding the mandate based upon the constitution and that what he did was related to politics - but I'm starting to think it wasn't weakness, but rather a fear for the court - not its reputation, but its existence.
Above, I wrote, "Maybe he [Roberts] feared Obama would decide to 'declare' the court ruling as wrong, and choose to ignore it, thereby nullifying the separation of powers and the constitution itself. That would amount to a kind of coup."
I think Roberts had what he saw as solid evidence that Obama and the progressives, with the tacit approval of the media would effectively "overthrow" the balance of power and begin setting explicit precedents for ignoring court decisions.
I don't know what his evidence might be (if this theory is right), but I still disagree with his actions, and I would rather have that fight, if that was the case, done explicitly.