WASHINGTON (AP) — Trying to earn a second chance, the senior administration official closest to the implementation of the health care law's malfunctioning enrollment website will answer questions from Congress at the start of a pivotal week.

Medicare Chief Marilyn Tavenner will be questioned Tuesday by the House Ways and Means Committee not only on what went wrong with HealthCare.gov, but also whether lawmakers can trust Obama administration promises to have things running efficiently by the end of November.

At stake is what the Republicans' partial government shutdown could not achieve: a delay of President Barack Obama's law expanding coverage for uninsured Americans. As a result of widespread sign-up problems, even some Democrats have joined Republicans in calling for a one-year postponement of the law's tax penalties for the remaining uninsured. The insurance industry warns that would saddle the new system with too many high-cost patients.