Aug. 20, 2012 -- Pressure mounted on Rep. Todd Akin to quit his Missouri Senate race today despite his repeated refusals to step down over his incendiary comments about rape.

Earlier in the day, moderate Republicans campaigning in bitterly contested battle ground states called on Akin to exit the race. By late in the afternoon, conservative elements of the party, including an influential super PAC and the Tea Party Express called on him to terminate his race for the good of the party.

Tea Party Express Chairman Amy Kremer said Akin's remarks that women rarely became pregnant from "legitimate rape" were "unfortunate and inappropriate" and added that they had become a distraction that would cost Republicans the chance to beat Democratic incumbent Sen. Claire McCaskill and ultimately any chance at winning the Senate.

"It is critical that we defeat Senator Claire McCaskill in November, but it will be too difficult to achieve that with Todd Akin as the conservative alternative. He should step down and give conservatives a chance at taking back the Senate in November," Kremer said in a statement.

The legal deadline for Akin to withdraw his name from the ballot is 5 p.m. Tuesday.

Akin, a Republican, insisted on Mike Huckabee's radio show today that he is staying in the race despite the furor over his comments that rape victims rarely get pregnant.

"If it's a legitimate rape, the female body has ways to try to shut that whole thing down," he said Sunday.

Akin apologized for the remark today and told Huckabee that he was "not a quitter," and still hoped to defeat McCaskill.

"I've really made a couple of serious mistakes here that were just wrong, and I need to apologize for those," he said.

"Let me be clear," Akin added. "Rape is never legitimate. It's an evil act that's committed by violent predators. I used the wrong words in the wrong way."

When asked by Huckabee to clarify what he meant by "legitimate rape," Akin said, "I was talking about forcible rape and it was absolutely the wrong word."

He later made similar comments on the Sean Hannity show.

CNN's Piers Morgan tweeted Monday that Akin, the "biggest name of the day," was to appear live on "Piers Morgan Tonight" Monday night. Morgan's show, however, opened at 9 p.m. with a shot of an empty chair.

Morgan said Akin's communications adviser agreed to book the interview and then pulled out "at the last possible moment ... leaving us and you looking at an empty chair." Morgan said that Akin is still welcome to appear on the show, or be "what we would call in England a gutless, little twerp."

After Akin insisted on staying in the race, the powerful and well-funded conservative super PAC American Crossroads, founded by former President George W. Bush's aide Karl Rove, pulled funding for his campaign, an attempt to exert pressure on him to quit or a tacit acknowledgement that he will now likely loose.

American Crossroads told ABC News that they "will not be spending in Missouri moving forward."

The group had spent $5.4 million and they had reserved at least $2.3 million more for the Missouri election.

Akin's initial statements sparked blowback from both parties.

Sen. Scott Brown, R-Mass, and Sen. Ron Johnson, R-Wisc., who are in competitive races in their own states, released scathing statements calling for Akin's withdrawal from the Senate race.

Akin would have to withdraw from the race by Tuesday in order for the Republican Party to field another candidate before November elections.

"As a husband and father of two young women, I found Todd Akin's comments about women and rape outrageous, inappropriate and wrong... Not only should he apologize, but I believe Rep. Akin's statement was so far out of bounds that he should resign the nomination for U.S. Senate in Missouri," Brown said.

"Todd Akin's statements are reprehensible and inexcusable," Johnson tweeted. "He should step aside today for the good of the nation."

Mitt Romney this morning called Akin's comments "inexcusable" and "wrong," but stopped short of calling for his resignation. A senior official in the Romney campaign said the candidate would not call on Akin to resign.

Shortly after Huckabee's interview, President Obama took the podium at a White House press briefing and called Akin's views "offensive."

"Rape is rape. The idea that we should be parsing and qualifying and slicing what type of rape we are talking about doesn't make sense to the American people and it certainly doesn't' make sense to me."

Obama said that Akin's comments demonstrated why "we shouldn't have politicians, most of whom are men, making decisions" about women's health.

He declined to comment specifically on Akin. "He was nominated by the Republicans of Missouri and I'll let them sort that out," Obama said.

Planned Parenthood President Cecile Richards denounced Akin's comment and it was an "egregious example" of legislators "making policy on women's health without understanding it."

"This statement by Mr. Akin is, I think, politics at its worst, ignoring basic medicine and science in pursuit of some political ideology," Richards said today during a conference call with reporters.

"I don't want to address whether he should resign, but I don't think he should be in office," she said.

Todd Akin Won't Quit Missouri Senate Race Over Rape Remark

Rep. Denny Rehberg, a Montana Republican, condemned him in the "strongest possible terms," calling his remarks "reprehensible" and adding "there is no such thing as a 'legitimate rape."

The comments were quickly seized on by Democrats who tried to link Akin to the presumptive Republican presidential ticket, putting Romney and Paul Ryan on the defensive.

"As a woman I'm really concerned that Paul Ryan doesn't understand that rape is rape," Democratic National Committee Chairwoman Rep. Debbie Wasserman-Schultz, D-Fla., said this morning on CBS, accusing Ryan and Akin of teaming up last year to pass legislation that would redefine rape.

"It is beyond comprehension that someone can be so ignorant about the emotional and physical trauma brought on by rape," Sen. Claire McCaskill,D- Mo., the Missouri incumbent who is fighting for her reelection said in a statement. "The ideas that Todd Akin has expressed about the serious crime of rape and the impact on its victims are offensive."

Additional reporting by ABC News' Emily Friedman, Shushannah Walshe, Devin Dwyer and Sunlen Miller