(CBS News) A top contractor for HealthCare.gov sent the Obama administration a memo three weeks before the program launched, warning that the site had not been sufficiently tested, CBS News has learned.
The lack of testing is one of many issues expected to come up when Health and Human Services Secretary Kathleen Sebelius testifies at a House committee hearing on Wednesday.
Sebelius was originally asked to testify last week, but she said she didn't have time, and the questions have only piled up since then, CBS News' Nancy Cordes reported on "CBS This Morning." Republican lawmakers want to know why she, and other administration officials appeared to be so surprised by problems with the website when they had gotten warnings about it in advance.
According to her prepared testimony, Sebelius will cast blame for Obamacare's bumpy rollout on a "subset" of the "many contractors our programs depend on to function," who she says "have not met expectations."
Marilyn Tavenner, who heads of the Centers for Medicare and Medicaid, the agency that oversaw those contractors, claimed on Tuesday that the website appeared to be ready to go right before the launch date.
Asked if there was any sense of the site's impending problems before the launch, Tavenner said, "No. ... There are always going to be issues with a new website, what I would call the customary glitches that you see, but no, not this."
That contradicts testimony from contractors who told lawmakers last week that they informed the administration two weeks before the launch that a test involving even low volumes of customers had crashed the website. And three weeks before the launch, the contractors sent the administration a report warning them that "there is not enough time built in to allow for adequate performance testing."
Rep. Fred Upton, R-Mich., who will chair Wednesday's hearing, says he wants to know more about what Sebelius was told and when.
Upton said, "Did they just not know it wasn't going to work, or did they know and refuse to pass up the line maybe even to her or to the president that, in fact, there was going to be a huge problem? When was it that they discovered that this was going to be a complete fiasco?"
Upton did not call for Sebelius to step down, but plenty of Republicans have -- 33 of them sent this letter to the president urging him to fire her.
Sen. Lamar Alexander, R-Tenn., said, "It's time for her to resign, someone else to take charge."
But Sebelius says she is staying put for as long as the president wants her to, claiming, "The majority of people calling for me to resign, I would say, are people I don't work for, and people who don't want this website to succeed in the first place.
Watch Nancy Cordes' full report above.