Put another way, Kathleen Sebelius has resigned and "Senior Administration Officials" are telling the media it is because of healthcare.gov.
You do not have a celebration event last week to celebrate 7 million sign ups and have Sebelius there to get credit then this week throw her under the bus because of a screw up that happened last October.
They have been standing with her since last October. They stood with her when the President's polling was nosediving and throwing her under the bus could have stopped the bleeding.
They are doing so now. Sebelius actually resigned last week and the President already has a nominee ready to roll out tomorrow.
Their internal polling must be terrible and they want her gone and the issue treated as "old news" before the GOP takes the Senate in November.
Sebelius leaving now is a pretty direct admission against interest that the Democrats expect to lose the Senate and do not see any events on the horizon to change that momentum. Now, they're just trying to slow the momentum down.