The government's healthcare.gov website launched on October 1 was supposed to spearhead President Barack Obama's sweeping health care reform, known as Obamacare.
The federal website serves 36 states, with the 14 other US states managing the system locally with their own websites.
But the websites have struggled with overloads, glitches and crashes, in a big embarrassment for the program.
"What breaks my heart... we're overshadowing how badly Obamacare has been rolled out," Republican Senator Lindsey Graham told ABC television's "This Week" program.
Until Congress ended the federal government shutdown in an eleventh-hour vote late Wednesday, the budget and debt crisis that paralyzed Washington largely obscured the health reform's troubled debut, even as Republican lawmakers were fighting to have it overturned.
"Government shutdown: Obamacare dodges a bullet," the Los Angeles Times summed it up in a headline earlier this week.
The site launch was a "gargantuan failure," said health industry consultant Bob Laszewski of Health Policy and Strategy Associates.
He estimated that during the federal website's first two weeks, only 10,000 Americans enrolled for insurance, with the websites in states handling their own exchanges getting mixed results.
According to The Washington Post, about 185,000 people had signed up by Wednesday on the state-based exchanges.
That's a far cry from the seven million Americans expected to enroll within the first year, according to estimates by the non-partisan Congressional Budget Office.
And more than 50 million Americans lack health care overall.
"The health insurance industry is shocked and extremely concerned," Laszweski told AFP.
"These people who are enrolling are their customers and (insurance companies) are very concerned that there will be service problems as we go forward and that they will be blamed for it... They are the ones that would have to lose the money."
Amid all the criticism, the Obama administration has so far refused to reveal how many Americans have signed up for insurance on its website, promising monthly data starting next month.
"This is one of the largest and most complex things we have ever done. Typically, a company launches a project like this in a city, then a few cities," said independent technology analyst Jeff Kagan.
"They figure out what doesn?t work right and they fix it before they roll it out nationwide. Why the government thinks it doesn't have to follow the same rules of common sense is a mystery."
Laszweski warned that unless the Obama administration moves fast to fix the technological glitches, people will lose confidence in Obamacare and the program could fold.
"Only the sickest people, who are willing to put up with all of the problems -- wait online for the website, wait on the phone for hours -- only the sickest people will sign up for the program and there won't be enough healthy people signing up to pay the costs of the unhealthy people," he said.
"The range of possibilities is anything between they get it fixed shortly to problems causing the entire program to collapse."
But White House spokesman Jay Carney stressed that Obama's reform extends far beyond the websites, and claimed that healthcare.gov had seen more than 17 million unique visitors since its launch.
"Although the glitches are unacceptable, so is the idea of leaving millions of Americans on their own, including families across the country who now have access to health care that they did not have," he said.
"Despite the glitches that we acknowledge and that absolutely must be fixed, people are getting on and enrolling. They are finding an enormous array of options available to them that weren't available to them in the past."
Obamacare supporters recall that major social programs such as Medicare health coverage for the elderly and Medicaid for the poor also faced difficulties at first but have since known solid success.
Aneesh Chopra, Obama's former chief technology officer, said the administration had expected about 60,000 people to sign up for an account -- and ended up getting about 250,000.
"They're looking to find ways to expand that capacity at that account creation step. It will be resolved over the next several weeks. I'm very confident of that," he told CNN.
"Hopefully, this will be a footnote in the challenges when we look back on the process."
On the very day the site launched, Obama pointed to tech giant Apple as an example.
"Consider that just a couple of weeks ago, Apple rolled out a new mobile operating system," he said.
"And within days, they found a glitch, so they fixed it. I don?t remember anybody suggesting Apple should stop selling iPhones or iPads -- or threatening to shut down the company if they didn?t."