Party leaders made it clear they wanted Missouri congressman Todd Akin to abandon his bid for a US Senate seat after he claimed women hardly ever get pregnant from what he called a "legitimate rape."
But the staunchly pro-life conservative said he wasn't going anywhere.
"I want to make one thing absolutely clear, and that is we are going to continue with this race for the US Senate," Akin said on the Mike Huckabee Show, a syndicated radio program.
"The defense of the unborn and a deep respect for life (are) important parts of who we are, and they're not things to run away from."
Akin's comments sucked the air out of the political debate just as Republican flagbearer Mitt Romney and his running mate Paul Ryan were looking to build a head of steam rolling into next week's national convention, where they will introduce themselves to millions of Americans during prime time.
It was not immediately clear just how much harm Akin has done the Romney campaign, but Republicans fear Akin's gaffe will jeopardize the party's efforts to woo female voters and to seize majority control of the Senate.
"The problem is that Akin's statement just reinforces (the) GOP's general problem with women," Republican strategist Mark McKinnon, a former top advisor for then-president George W. Bush, told AFP.
"It appears Republicans recognize that and are unanimous in calling Akin to get out of the race."
The party denied Akin about $5 million in campaign funding and political action committee Crossroads GPS said it was halting its spending in Missouri, including $2.3 million it had committed to advertising in the state.
Akin tried to sound repentant in a new campaign ad in which he sought forgiveness from voters.
"Rape is an evil act. I used the wrong words in the wrong way, and for that I apologize," he said, in a 30-second spot in which simply featured a grave looking candidate addressing the camera directly.
"I have a compassionate heart for the victims of sexual assault, and I pray for them. The fact is, rape can lead to pregnancy. The truth is, rape has many victims."
Akin, who is running against Claire McCaskill, perhaps the most vulnerable incumbent Democrat in the Senate, triggered outrage on Sunday when he falsely said a woman's body can block an unwanted pregnancy.
Astonished Republicans, including Romney who squares off against President Barack Obama in November's election, denounced the remarks as offensive and inexcusable, and the party's leadership quickly abandoned him.
Even as Republicans were scrambling to douse the flames, party leaders were hashing out a platform to be unveiled at next week's convention.
They were reportedly set to include a "human life amendment" that would outlaw abortion while making no explicit exemptions for rape or incest.
CNN reported it had obtained a draft which declares that the "unborn child has a fundamental individual right to life which cannot be infringed."
"We support a human life amendment to the Constitution and endorse legislation to make clear that the Fourteenth Amendment's protections apply to unborn children," the draft said, according to CNN.
Democrats were eager to see Akin stay in the race, as it would only highlight a debate over abortion and women's rights that Democrats believe will hurt Romney, who is already behind in support from female voters.
"If this isn't a war on women, I don't know what is," Senator Barbara Mikulski, the longest-serving woman in the US Congress, said in a statement.
Obama, who denounced Akin's comments on Monday, was campaigning in the battleground state of Ohio, while Romney was en route to Texas for fundraisers.
With 11 weeks to go before the election, both camps are preparing spending blitzes, and official figures showed Tuesday that Romney had a clear advantage.
In a monthly report for July filed with the Federal Election Commission, Obama claimed reserves of $124 million between the president's campaign and his Democratic Party, while the Romney campaign earlier said it had $186 million.