MILLIONS of Americans negotiating America’s health care system know all too well what the waiting room of a doctor’s office looks like. Now, thanks to HealthCare.gov, they know what a “virtual waiting room” looks like, too. Nearly 20 million Americans, in fact, have visited the Web site since it opened three weeks ago, but only about 500,000 managed to complete applications for insurance coverage. And an even smaller subset of those applicants actually obtained coverage.

For the first time in history, a president has had to stand in the Rose Garden to apologize for a broken Web site. But HealthCare.gov is only the latest episode in a string of information technology debacles by the federal government. Indeed, according to the research firm the Standish Group, 94 percent of large federal information technology projects over the past 10 years were unsuccessful — more than half were delayed, over budget, or didn’t meet user expectations, and 41.4 percent failed completely.

For example, Sam.gov, a system for government contractors developed by I.B.M. that started in 2012, has cost taxpayers $181 million and is just now beginning to work as expected. Before that, a new version of USAJobs.gov landed with a thud, after years during which millions were spent. In 2001, the F.B.I. started a virtual case file system, and after dumping the project, renaming it, and finding new vendors to build it, the project, “Sentinel,” managed to see the light of day just last year.

Clearly, these failures — though they are not as well known to the public — extend far beyond Barack Obama’s presidency. But this latest stings more than the others. Perhaps that’s because it comes from a president who is seen as a transformational figure, who has had to watch his signature achievement be held hostage by that most banal of captors: a clunky computer system.