WASHINGTON — The second sign-up season under President Barack Obama’s health overhaul opened Saturday, with hopes that this time consumers will have a positive experience.

But the fear is that entrenched political opposition and renewed legal challenges may yet collapse the program that’s bringing health care to millions of previously uninsured Americans. The administration can’t afford another technology meltdown.

With 7 million paying customers in new insurance markets, the Affordable Care Act has shown it is helping to reduce the number of uninsured. Insurers, not known for altruism, have stuck with the fledgling program despite ongoing technical headaches with the HealthCare.gov website. More companies are participating for 2015, a sign they see a business opportunity.

The administration said late Friday that some HealthCare.gov functions would be turned off for several hours in the transition to the start of sign-up season. The website appeared to functioning early Saturday.

“Obamacare” is still struggling to win hearts and minds. The latest Associated Press-GfK poll finds that, if forced to choose between repealing the law and implementing it as written, 56 percent of Americans would repeal it completely. Only 41 percent would carry it out.