Welcome to Health Reform Watch, Sarah Kliff’s regular look at how the Affordable Care Act is changing the American health-care system — and being changed by it. You can reach Sarah with questions, comments and suggestions here. Check back every Monday, Wednesday and Friday afternoon for the latest edition, and read previous columns here.

Housekeeping announcement: Starting this month, you can sign up to get Health Reform Watch straight to your inbox! Just enter your information here, and you'll be all set. 

Medicare administrator Marilyn Tavenner (Center for Medicare and Medicaid Services) Medicare administrator Marilyn Tavenner (Centers for Medicare and Medicaid Services)

As Medicare administrator, Marilyn Tavenner oversees a $1 trillion agency that provides insurance coverage to 90 million Americans -- and, for the past three years, has overseen the health law's rollout.

And as recently as late September, Tavenner predicted that the Affordable Care Act would have a smooth October launch.

"I talked to Marilyn a lot before the rollout, and I think she was surprised by how it's gone," said Tom Scully, a former Medicare administrator and longtime colleague of Tavenner's. "She seemed pretty confident it would work.

"She said, 'I'm going to be incredibly busy the next 10 days.' "

We now know that the rollout of HealthCare.gov has been anything but smooth: Nearly one month after launch, many consumers are still unable to purchase insurance coverage through the new insurance marketplace. The Obama administration has promised the Web site will be fixed by the end of November, two months after the Oct. 1 start.

On Tuesday, Tavenner will be the first Obama administration official to testify before Congress on the Affordable Care Act's launch. She is likely to face a barrage of questions about the circumstances that lead to the Web site's faulty launch -- and the Obama administration's prior claims that they were on track for a successful launch.

"We will focus on oversight of why the testing did not occur, why the administration told this committee repeatedly that they were on track when they were not, the uncertainty this is causing for Americans trying to sign up, wondering if their doctor will still take their coverage, seeing cancellations of their current health-care plan," said a spokeswoman for the Ways and Means Committee, which will hold the hearing.

Health law contractors, at a House Energy and Commerce Committee hearing last week, were quick to point the finger at Tavenner's agency for leaving too little time for testing the Web site.

"CMS had the ultimate decision to go live or not go live," Cheryl Campbell, vice president of CGI Federal, testified at that hearing. "At CGI we were not in a position to make that decision. We were there to support the client. It's not our position to tell clients whether to go live or not go live."

Whether Tuesday's hearing moves in a similar direction isn't clear. As Medicare's first confirmed head in in nearly a decade, Tavenner during her short tenure has enjoyed unusually strong bipartisan support from legislators, who see the former hospital executive as a pragmatic pick for the Medicare agency.

Republican legislators have focused more on Health and Human Services Secretary Kathleen Sebelius, with some calling for her resignation. The Centers for Medicare and Medicaid Services is a division within HHS.

"The problems with Obamacare transcend the Web site or one office within HHS," said Megan Whittemore, a spokeswoman for House Majority Leader Eric Cantor (R-Va.).

Cantor supported Tavenner's nomination this winter; the two came to know each other when he was involved in politics and she was running a local hospital.

"Tavenner's recent appointment was encouraging, but this law is unfixable," Whittemore continued. "More concerning is Secretary Sebelius’s mismanagement since Obamacare became law."

Tavenner joined the Obama administration in April 2010 after a decades-long career in Virginia hospitals. She began her career as an intensive-care unit nurse in Richmond. One of her former colleagues recalled a particularly harrowing night, when Tavenner helped save a patient who had been presumed dead on arrival at the hospital.

“That’s about as tough of a case as you get, a girl who was thought to be dead,” Erik Swensson, a surgeon who had worked with Tavenner, previously recounted to The Post. “Marilyn was very supportive in everything, asking what we were doing, whether I was going to take her back to surgery. We came up with a game plan, and it was right on target. We used about 60 units of blood, but [the patient] ultimately walked out of the hospital.”

Tavenner rose from the intensive-care unit to become her hospital's chief nursing officer and then the chief executive of two Virginia hospitals owned by the Hospital Corporation of America, one of the country's largest hospital chains. In 2004, she was promoted to a national position with HCA and served as the company's president of outpatient services.

Tavenner left the corporate world the following year, when then-Virginia Gov. Tim Kaine appointed her to serve as the state's secretary of health and human resources. There, she saw her top priorities as assisting the uninsured, mental health services, Medicaid reform, aging and health-care workforce issues.

"Marilyn's background as a leader in hospital administration and Medicaid has been a real asset," said Mark McClellan, one of President George W. Bush's Medicare heads, who oversaw the implementation of the agency's prescription drug program, Part D.

Obama twice nominated Tavenner to run the Medicare agency, first in November 2011 and again in January 2013, after Senate Republicans pledged to block the appointment of the president's previous nominee, Don Berwick.

While Berwick's nomination became a political flash point -- Republican senators seized on his remarks praising Britain's National Health Service -- Tavenner had a smooth path forward. The Senate supported Tavenner's nomination by a 91 to 7 vote in May, making her the first confirmed Medicare chief in seven years.

"There's generally a positive feeling about her, and I certainly share that," said Bruce Vladek, a former Clinton Medicare head and senior adviser at health-care consulting firm Nexera. "She's very accessible, very direct and very open. She's clear-sighted about aims and priorities."

Vladek spoke with Tavenner earlier this month about a health-care issue not related to the health law rollout.

"I was clearly talking to an extremely tired and somewhat stressed person," he says. "She was still very well-informed and very much on point. She knew exactly the state of where the issue was, even though we didn't agree on everything."

With reporting from Amy Goldstein

KLIFF NOTES: Top health policy reads from around the Web.

HealthCare.gov was stymied by a lack of federal direction. "As it becomes clear that no single leader oversaw implementation of the health law's signature online marketplace — a complex software project that would have been difficult under the best circumstances — the accounts of more than a dozen current and former officials show how a disjointed bureaucracy led to the site's disastrous Oct. 1 launch." Christopher Weaver and Louise Radnofsky in The Wall Street Journal

Web site troubles might dissuade the young and healthy from signing up. "Lack of awareness makes it all the more important that those who do know about HealthCare.gov — and try to purchase insurance there — are not dissuaded because of the glitches, the analysts said. Older and sicker Americans have a stronger incentive to keep trying to sign up despite the clunky site, they said." Annie Lowrey in The New York Times.

There is one part of the health law's technology that has worked: The data hub. "When the law's critics raise fears of security breaches, they're talking about the data hub. The hub transmits massive amounts of information about people seeking health insurance, drawing from several federal agencies and communicating with every state's insurance marketplace. It was initially seen as one of the most likely places for problems to arise in the enrollment process. So far, though, the reviews are positive." Sam Baker in National Journal.