Obama speaking in Colorado. REUTERS

President Obama and Mitt Romney are again trading barbs over the Affordable Care Act's mandate that insurers cover contraception, reviving a months-old debate pitting women's health against religious liberty.

Obama invoked the issue during a campaign stop in Colorado, where he warned that Romney's policies were "more suited to the 1950s than the 21st century." The president was introduced by Sandra Fluke, a Georgetown Law School graduate who became enmeshed in the debate after she defended the insurance mandate and was denounced by conservative talk show host Rush Limbaugh.

Fluke's presence offered a clear reminder that the Obama campaign has not forgotten about the controversy, and will continue to appeal to female voters by citing Republican opposition to the Affordable Care Act. Polls show that Obama retains a substantial lead among female voters, helping to counteract Romney's advantage among working-class white men.

"The decisions that affect a woman's health aren't up to politicians or insurance companies, they're up to you," Obama said during a Denver speech.

Obama also cited Romney's vow to defund Planned Parenthood and his joining Republicans who closed ranks in decrying the insurance mandate.

"He joined the far right to support a bill that would allow an employer to deny contraceptive coverage to their employees," Obama said. "Let me tell you something, Denver - I don't think your boss should control the care you get. I think there is one person who should make decisions on your healthcare, and that person is you."

But the Romney campaign is not backing off its critique of the birth control requirement, doubling down with a new advertisement charging that "President Obama used his health care plan to declare a war on religion." The spot then shows a clip of Romney praising Pope John Paul II during a recent visit to Poland.

"When religious freedom is threatened, who do you want to stand with?" the narrator asks.

The ad represents a rare foray into social issues for the Romney campaign, which has worked to make the election a referendum on Obama's handling of the economy. The Republican National Committee kept up that effort on Wednesday, saying ahead of Obama's speech that women have suffered under his administration.

"Today, unemployment among women is higher than when President Obama took office," RNC Co-Chairwoman Sharon Day said in a statement. "More women are out of work in the Obama economy, and the few jobs that are created go disproportionately to men."