The poll by the nonpartisan foundation found that 54% of those surveyed said the Supreme Court should rule against the mandate while only 17% said the court should uphold it and 29% either didn’t know or didn’t answer.

Republican opposition to the Democrats’ 2010 health care overhaul law is intense, with 73% of Republicans having an unfavorable view of it. By contrast, 62% of Democrats view it favorably.

The survey also found that most Republican voters don’t agree with the attack on GOP presidential candidate Mitt Romney that the health care law he signed as governor of Massachusetts is similar to the federal law. Some 30% said they felt Mr. Romney’s views on health care were akin to President Barack Obama’s, but almost half said the former governor’s views are different, and 22% didn’t answer.