A new radio ad by the Obama campaign accuses John McCain of supporting an amendment to the U.S. Constitution banning abortion and re-airs McCain’s support for overturning Roe v. Wade, Politico reports. The ad campaign exemplifies a shift over previous election cycles where Republicans have used the hot-button issue to hammer Democrats. However, polling suggests that most Americans are more closely aligned with Obama’s policies on the issue and that a significant number of moderate McCain backers erroneously think he is pro-choice.

Half of Americans polled think that abortion should be legal most of the time. Less than a third support McCain’s position of making abortion illegal except in cases of incest, rape or health risks to the life of the mother. Around 18 percent of Americans share the view of McCain’s running mate Sarah Palin that abortion should be illegal in all cases.

While the majority of Americans support Obama’s position on the issue, only 20 percent of voters say the issue will sway them toward or away from a particular candidate.

The radio ads are running in a number of states where the candidates are closely matched: Indiana, Pennsylvania, and New Hampshire.

Here’s a transcript of the radio spot:

OBAMA: I’m Barack Obama, candidate for president, and I approved this message.

VAL BARON: As a nurse practitioner with Planned Parenthood, I know abortion is one of the most difficult decisions a woman will ever make. I’m Val Baron. Let me tell you: If Roe v Wade is overturned, the lives and health of women will be put at risk. That’s why this election is so important. John McCain’s out of touch with women today. McCain wants to take away our right to choose. That’s what women need to understand. That’s how high the stakes are.

ANNCR: As president, John McCain will make abortion illegal. McCain says quote, “I do not support Roe v. Wade. It should be overturned.” And listen to McCain’s answer on Meet the Press:

RUSSERT: “A constitutional amendment to ban all abortions. You’re for that?”
McCAIN: “Yes, sir.”

VAL BARON: We can’t let John McCain take away our right to choose. We can’t let him take us back.

ANNCR: Paid for by Obama for America.