Americans have a dimmer view of the health care law now than they did when Obama triumphantly signed it three years ago, according to monthly tracking polls by the Kaiser Family Foundation. The public’s divided view and relentless Republican attacks have made it easier for governors and state legislators to balk at cooperating with the law. It is designed to provide coverage for millions of Americans who haven’t qualified for Medicaid in the past and don’t get insurance through their employers.

That could have a cascading effect: Resistance by the states will make it harder for the law to work as promised when Medicaid expands next year and the health-insurance marketplaces where the uninsured can shop for plans open this fall.

That could fortify the arguments of those who warned the law was a mistake from the start and threaten fundamental provisions of it down the road.

“For most of the Obama administration, the thought was the bill was passed and it’s over,” says Robert Blendon, a Harvard professor and influential analyst who supports the law. The president understandably turned his attention to the fragile economy, and the most far-reaching expansions of coverage were delayed until 2014 — leaving the door open for opponents to warn of calamity ahead. “By the time they returned to it,” Blendon says of White House officials, “opinions were really embedded.”