US President Barack Obama aggravated a culture war battle over contraception as he wooed women voters, warning that Mitt Romney's Republicans would turn back the clock to the 1950s.
Obama cranked up his re-election bid in the swing state of Colorado -- where a poll showed his White House foe Romney up by five points -- vowing to protect women's health rights enshrined in his historic health care law.
"When it comes to a woman's right to make her own health care choices, they want to take us back to the policies more suited to the 1950s than the 21st Century," Obama said, in a stinging attack on Republicans.
Obama argued that Romney's vow to repeal the law would tear away hard-won care for women, including in some cases free birth control, breast cancer screenings and other preventive care insurance firms must now cover.
"The decisions that affect a woman's health, they are not up to politicians, they are not up to insurance companies, they are up to you," he told a raucous rally in Denver, against a backdrop of female supporters.
"You deserve a president who will fight to keep it that way. That's the president I have been. That is the president I will be if I get a second term."
Obama appeared arm in arm with law graduate Sandra Fluke, who was caught in a political maelstrom and branded a "slut" by conservative talk show firebrand Rush Limbaugh this year after saying students should get free contraception.
"If Mr Romney can't stand up to extreme voices in his own party, then we know he will never stand up for us, and he won't defend the rights that generations of women have fought for," Fluke said.
"We must remember that even though it is 2012, we are still having the debates that we thought were won before I was even born."
The president also spoke movingly about the women in his life, including his mother, who died from cancer aged 52 and never got to meet her granddaughters Malia and Sasha or see her son become president.
"I often think about what might have happened if a doctor had caught her cancer sooner, or if she had been able to spend less time focusing on how she was going to pay her bills and more time on getting well," Obama said.
He also noted the two and three year anniversaries of his nominees Sonia Sotomayor and Elena Kagan taking their seats on the Supreme Court -- and warned the next president would likely get to make more appointments.
Romney countered Obama's attack by unveiling his "Women for Mitt" coalition, which will be led by his wife, Ann, and by arguing that female voters had suffered terribly in the slow economic recovery for which he blames Obama.
Ann Romney said her husband "knows how to turn around this economy so that it will better serve the interests of women and families across America."
Romney will also showcase prominent women at this month's Republican convention, including former secretary of state Condoleezza Rice.
Obama's gambit on Wednesday reflected his strategy of trying to wrest the election debate away from an exclusive focus on the economy -- which Romney sees as his best chance for victory on November 6.
The president made his pitch in Colorado, a crucial Rocky Mountain swing state, on a day when a new poll by Quinnipiac University found him trailing Romney by 45 to 50 percent in the battleground state, which he won in 2008.
Women, who represent about 53 percent of the US electorate, backed Obama 56-43 percent over John McCain in the 2008 election.
A recent New York Times/CBS poll found Obama leading Romney among single women by 29 points, but married women historically lean towards Republican candidates.
So gender gap politics will play out all the way to the election, as Obama seeks to lock in his slender lead in most national polls and swing state surveys.
The issue of contraception was thrust into the 2012 election campaign early this year after Republicans claimed Obama's provision requiring organizations to offer free contraception on employee health plans was a war on religion.
Obama sought to defuse the row by exempting religious organizations. But he stuck by the principle that all women should have free access to such services, putting the onus on insurance firms to offer women working for religious employers such as Catholic hospitals free birth control coverage.