Those delays — due to technological snags with enrollment websites, bureaucratic tangles at state Medicaid programs and a surge of applicants — betray Barack Obama’s promise to expand access to health care for some of the nation’s most vulnerable citizens.

As a result, some low-income people are being prevented from accessing benefits they are legally entitled to receive. Those who face delays may instead put off doctors appointments and lose access to their medicines, complicating their medical conditions and increasing the eventual cost to U.S. taxpayers.

Democratic lawmakers who have promoted the law’s historic coverage expansion are wary of acknowledging problems that hand opponents of the Affordable Care Act another rhetorical weapon, said Robert Blendon, a professor at Harvard University School of Public Health and Kennedy School of Government.