The rollout of the Affordable Care Act this month should have been a moment of singular triumph for President Obama and Democrats in Congress. Instead, the administration’s abysmal failure to anticipate the level of demand for health insurance over the Internet has become a major embarrassment that disappoints the law’s defenders and heartens its critics.

The administration’s failure is hard to fathom. Ever since he was elected in 2008, Mr. Obama has insisted in speech after speech that Americans, especially those unable to obtain health insurance, demanded reform. The Affordable Care Act would fix that problem, he said.

Yet on opening day, when the predicted demand materialized and armies of people wanted to sign up, the system crashed because it could not cope with the large numbers of applicants. Didn’t anyone in the administration see this coming?

Sure, some opening-day jitters are to be expected. Creating a website (HealthCare.gov) to manage a revolutionary change in the nation’s healthcare structure is a huge technological lift. Some stumbles are to be expected. But this goes beyond a mere glitch.

The online portal for uninsured Americans in 36 states that don’t have their own exchanges — including Florida — has malfunctioned now for three weeks. It was expected to draw at least 7 million people during the sign-up period for federally subsidized private insurance for 2014, but many of those who have tried — perhaps most — have been frustrated by the system’s failure.

The White House has said that 500,000 people have filled out applications as of last week, but it has withheld figures for enrollment —those who purchased coverage.

On Thursday, a software contractor for the government website testified before Congress that his company warned the administration about performance risks before it opened on Oct. 1, saying there was too little time for testing.

“We didn’t see the full integrated end-to-end system until a couple of days leading up to the launch,” contractor Andrew Slavitt said. “Months would be nice.”

Indeed, as far back as July, the head of Florida Blue, formerly Blue Cross Blue Shield, told the Editorial Board that the two-month testing period before the rollout was far too short. “In the private sector, we would have required six months, at least,” said Patrick J. Geraghty, adding that he had warned the administration.

Apparently, all such warnings went unheeded. Belatedly, there’s a rush to make fixes. Amid the collateral damage is the Spanish-language version of the system (CuidadoDeSalud.gov). The mid-October opening of its main functions is not yet up and running, and no one can say for certain when it will be ready.

Contractors testified Thursday that fixes are under way to ensure that everyone can sign up in time to meet enrollment deadlines. At the same time, the administration extended the deadline for six weeks, until March 31, and brought in a crisis expert with experience in government and corporate America to manage the overhaul.

“There’s no excuse for the problems,” Mr. Obama said this week. He’s certainly right about that. But he has to do more than talk about it: Demand a thorough examination of how this went wrong and fire whoever is responsible.

And most important, get the system up and running. This is the president’s biggest legislative achievement, but until those who have been eagerly anticipating its arrival can sign up, frustration will continue to grow.