Senators grill Obamacare administrator over healthcare.gov WASHINGTON -- The top Obamacare administrator told a Senate committee that setbacks will not hamper overall enrollment in the Affordable Care Act, which she said was expected to start slowly and then grow before the 2014 deadline to carry insurance coverage. Democrats joined Republicans on Tuesday grilling Marilyn Tavenner, the chief of the Centers for Medicare & Medicaid Services, which is overseeing the website for the Health and Human Services Department. "There has been fear, doubt and a crisis of confidence," said Sen. Barbara Mikulski (D-Md.). Officials have worried that if uninsured Americans decline to purchase insurance policies through the online marketplace, the Obamacare system could collapse. Tavenner said outreach to enroll more Americans will begin in December, once the website problems are fixed by the end of the month. She testified that the administration had always expected a slow start to enrollments, as happened when Massachusetts launched a similar statewide healthcare system under then-Gov. Mitt Romney. "We always assumed based on the Massachusetts experience the initial sign-up would be very slow," Tavenner said. We do not think it will impact the timeline. The deadline for Americans to carry insurance is March 2014. The website went dark for 90 minutes Monday, and will be down four hours every night as improvements are made, officials said. Tavenner reiterated the administration's promise that the site, which launched Oct. 1 as a centerpiece of the new law, will be running more smoothly by the end of the month. The administration has doubled the number of servers, and Tavenner said it now takes one second for pages to load, rather than eight. The site can now process 17,000 registrants an hour - five per second - "with almost no errors," Tavenner said. She rejected calls to re-do the site from scratch. "This is weeks, not months," she said about the timeline for improvements, "and we are not rewriting the architecture." Twitter: @lisamascaroinDC