This very good article from NYT reporters Sheryl Stolberg and Michael Shear sets the stage early on:

HealthCare.gov, the $630 million online insurance marketplace, was a disaster after it went live on Oct. 1, with a roster of engineering repairs that would eventually swell to more than 600 items. The private contractors who built it were pointing fingers at one another. And inside the White House, after initially saying too much traffic was to blame, Mr. Obama’s closest confidants had few good answers.

It is a fairly long article, but informative, and the full article is HERE.