Obamacare has led to health coverage for millions more people.... At least 9.5 million previously uninsured people have gotten health insurance since Obamacare started, surveys and reports show.

WASHINGTON — President Obama's healthcare law, despite a rocky rollout and determined opposition from critics, already has spurred the largest expansion in health coverage in America in half a century, national surveys and enrollment data show.

As the law's initial enrollment period closes, at least 9.5 million previously uninsured people have gained coverage. Some have done so through marketplaces created by the law, some through other private insurance and others through Medicaid, which has expanded under the law in about half the states.

The tally draws from a review of state and federal enrollment reports, surveys and interviews with insurance executives and government officials nationwide.

• Also
• Covered California Q&A: Is Monday still the deadline to enroll?
• How Covered California is measuring up
• Insurers already calculating 2015 premiums as Obamacare kicks in
• L.A. County grapples with healthcare for remaining uninsured
• Fighting for Obamacare through stage IV cancer

The Affordable Care Act still faces major challenges, particularly the risk of premium hikes next year that could drive away newly insured customers. But the increased coverage so far amounts to substantial progress toward one of the law's principal goals and is the most significant expansion since the creation of Medicare and Medicaid in 1965.

The millions of newly insured also create a politically important constituency that may complicate any future Republican repeal efforts.

Precise figures on national health coverage will not be available for months. But available data indicate: more