WASHINGTON — President Barack Obama celebrated when sign-ups for his health care law topped 8 million, far exceeding expectations after a slipshod launch. Most Americans, however, remain unimpressed.

A new Associated Press-GfK poll finds public opinion continues to run deeply negative on the Affordable Care Act. Forty-three percent oppose the law, compared with 28 percent in support.

The pattern illustrates why the health care law remains a favored target for Republicans seeking a Senate majority in the midterm elections.

The poll does have a bright spot for the administration: Those who signed up for coverage aren’t reeling from sticker shock. Most said they found premiums in line with what they expected, or lower.

But even that was diminished by another finding: More than one-third of those who said they or someone in their household tried to enroll, were ultimately unable to do so.