The second major contributor were all the decisions to maximize coverage. These decisions have been made all along the way, so they have preceded that website debacle and could be considered the single major contributor to the Obamacare failure if it happens. The decision to maximize coverage lead to higher policy costs, higher subsidies, and more people deciding to flout the law and go without insurance. Maximizing coverage has its strong points too, but they don't matter if the strategy collapses universal coverage.
If you want to provide universal coverage, doesn't it make sense to do so at an attainable level? If you're going to invite the entire neighborhood to a cookout, you may have to settle for serving hot dogs and hamburgers, not filet mignon and king salmon.
Maybe Obamacare will work out, and in a year or two we'll have settled into it, have some minor grumbles, but generally be satisfied. But the risks were underestimated by the administration. They should have been more careful and, ahem, more conservative because universal coverage is a big fucking deal, and a major step forward in fairness. But Dems aren't careful like that, which is one reason I rarely admit my party affiliation anymore.
If Obamacare sinks, I'll give most of the blame to the Dems. The GOP of course will deserve some for constantly barraging or undermining the program instead of helping improve it. But it will be the Dems who sank their own ship.