The senior Obama administration official closest to the implementation of the health care law's dysfunctional website faces tough questions today from Congress at the start of a pivotal week.

U.S. Capital Building (Architect of the Capitol)

Medicare Chief Marilyn Tavenner will be questioned by the House Ways and Means Committee on what went wrong with HealthCare.gov, and whether she saw any of it coming.

Lawmakers also want to know whether they can trust administration promises to have things running efficiently by the end of November.

At stake is what the 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.

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