Barack Obama has launched a broadside against John McCain’s opposition to abortion rights and moved one of the most divisive issues in modern American politics to the airwaves on a large scale for the first time in this presidential campaign.

Obama’s new radio ad, airing widely in at least seven swing states, tells voters McCain “will make abortion illegal.” It’s airing as McCain courts female voters with the addition of the staunchly anti-abortion governor of Alaska, Sarah Palin, to his ticket.

Democrats had, until now, sought to appeal to women primarily on economic issues such as health care and workplace discrimination; abortion rights were hardly mentioned at the Democratic National Convention in Denver last week. But women’s rights groups have been urging Obama to attack McCain on the issue, pointing to polling showing that some women who support McCain think he supports abortion rights. In fact, the Arizona senator has long supported a ban on abortions, with exceptions for victims of rape and incest, and for pregnancies that threaten the life of the mother. Palin has an even firmer anti-abortion stance: She would require rape and incest victims to carry their pregnancies to term.

“Let me tell you: If Roe vs. Wade is overturned, the lives and health of women will be put at risk. That's why this election is so important,” says the nurse-practitioner who narrates Obama’s ad. “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.”

An announcer then claims that “as president, John McCain will make abortion illegal,” before playing an exchange on "Meet the Press" in which McCain told moderator Tim Russert that he favors “a constitutional amendment to ban all abortions.”

“We can't let John McCain take away our right to choose. We can't let him take us back,” says the ad.