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Missouri Rep. Todd Akin resisted a united front of Republican Party pressure Tuesday to drop his Senate bid following controversial comments on rape, as Mitt Romney and other party power brokers isolated him amid concern he'd hurt Republicans' chances of winning control of the Senate.

Democrats have already used Akin's comments -- in which he claimed women's bodies can fend off pregnancy in cases of "legitimate rape" -- to raise campaign money and cast other Republicans as insensitive toward women. GOP leaders tried to minimize the damage by first condemning Akin's remarks, and then one after another urged Akin to get out of the race.

Akin, though, resisted. He told Fox News host Mike Huckabee on his radio show Tuesday afternoon that he's staying.

"I believe that we can win this," Akin said, citing a "tremendous outpouring of support" from individual donors even as party heavyweights freeze him out. Akin called the fallout a "little bit of an overreaction."

Going forward, Akin appears to be on his own. He can still opt to withdraw from the race, but because he missed a Tuesday deadline, he would have to seek a court order and pay the costs of reprinting ballots. Tuesday was the last day Akin could withdraw without court intervention and penalty payments.

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    There's not much the Republican Party can do about Akin's defiance. Asked about their options, one Missouri Republican source told Fox News there are "none really -- we examined the alternatives a few years ago when a convicted felon won the nomination for state auditor."

    Barring a write-in campaign by a third candidate, Akin could remain the chief opponent to Missouri Sen. Claire McCaskill in the fall. And that became a suddenly uphill battle as GOP leaders made clear that Akin will not be receiving their support.

    The National Republican Senatorial Committee, in addition to well-funded conservative groups, reiterated that stance Tuesday. "If he continues with this misguided campaign, it will be without the support and resources of the NRSC," the NRSC said in a statement.

    Romney added his voice after five former and present Missouri Republican senators urged Akin to step aside. In a statement released Tuesday afternoon, they said his presence does not serve "the national interest."

    "The issues at stake are too big, and this election is simply too important. The right decision is to step aside," they said. The statement came from Missouri Sen. Roy Blunt, and former Sens. John Ashcroft, Kit Bond, John Danforth and Jim Talent.

    Romney released a statement late Tuesday saying: "As I said yesterday, Todd Akin's comments were offensive and wrong and he should very seriously consider what course would be in the best interest of our country.  Today, his fellow Missourians urged him to step aside, and I think he should accept their counsel and exit the Senate race."

    Akin had earlier released an ad pleading for forgiveness from voters. In the ad, Akin looked into the camera and addressed the controversy surrounding his remarks.

    "Rape is an evil act. I used the wrong words in the wrong way and for that I apologize," he said in the ad. "As the father of two daughters, I want tough justice for predators. 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.

    "The mistake I made was in the words I said, not in the heart I hold. I ask for your forgiveness," he said.

    The Missouri Senate race is considered key to Republicans' chances of retaking the Senate for the 2013 session.

    Democratic groups across the country have tried to exploit Akin's comments. They seized on a decision Tuesday by a Republican Party platform committee approving a plank that called for an amendment to outlaw abortion -- without a stated exception for rape or incest. It was similar to platforms adopted in the past and Republican sources indicated it had nothing to do with Akin, but the Obama campaign nevertheless put out a statement accusing Republicans of having passed "the Akin amendment."

    Akin made the controversial remarks in an interview with Fox affiliate KTVI. He claimed a woman's body can typically fend off pregnancy during a "legitimate rape," as he argued against allowing abortions in cases of rape, claiming such pregnancies are uncommon in the first place.

    "It seems to me first of all, from what I understand from doctors, that's really rare," Akin told KTVI. "If it's a legitimate rape, the female body has ways to try to shut that whole thing down."