Republican presidential candidate Mitt Romney and the entire GOP national political apparatus launched a swift and relentless crusade against one of their own Monday, seeking to drive Rep. Todd Akin out of the U.S. Senate race in Missouri after his controversial comments on rape and pregnancy threatened the party with widespread political harm.

“Congressman Akin’s comments on rape are insulting, inexcusable and, frankly, wrong,” Romney told the National Review early Monday. His remarks were soon followed by calls from two GOP senators to withdraw and statements later from Senate Minority Leader Mitch McConnell (R-Ky.) and Sen. John Cornyn (R-Tex.), the party’s chief Senate campaign strategist, meant to push Akin aside.

Akin’s Senate race in Missouri against the embattled Democratic incumbent, Sen. Claire McCaskill, has been regarded as one of the most competitive in the country and one of the best opportunities for the GOP to grab a seat.

But, fearing the Akin controversy may cost them more than just that one race, Romney and Senate GOP leaders urged Akin to step aside and pulled funds from what they once considered a sure pickup. Democrats hope to capi­tal­ize on Akin’s troubles, but it was the Republican response that brought the most pressure to bear. GOP leaders made the decision early Monday to try to forcefully push Akin out well before next week’s national party convention, leaving his campaign in tatters by day’s end.

Sen. Ronald H. Johnson (R-Wis.), a social conservative and tea party leader after his 2010 victory, also called for Akin to drop out: “Todd Akin’s statements are reprehensible and inexcusable. He should step aside today for the good of the nation.”

The efforts at damage control were somewhat hindered by Akin’s decision to resist the push to get him out of the race.

By midday Monday, Akin had dug in for a fight, giving no public sign that he would withdraw.

“The good people of Missouri nominated me, and I’m not a quitter,” Akin told Mike Huckabee, the former Arkansas governor who now hosts a radio show. “My belief is, we’re going to take this thing forward. And, by the grace of God, we’re going to win this race. To quote my old friend John Paul Jones, ‘I’ve not yet begun to fight.’ ”

Akin’s media tour to defend himself included a radio appearance with conservative host Sean Hannity. He did not show up for a planned appearance with CNN’s Piers Morgan, who opened his show with an empty chair where Akin was supposed to be sitting.

The comments that sparked the fury aired Sunday on a St. Louis TV station. Akin, an engineer by training, was asked about his staunch opposition to abortion even in the case of women getting pregnant after a rape.

“From what I understand from doctors, that’s really rare,” Akin said. “If it’s a legitimate rape, the female body has ways to try to shut that whole thing down. But let’s assume that maybe that didn’t work or something, I think there should be some punishment, but the punishment ought to be of the rapist, and not attacking the child.”

After backtracking from his comments later Sunday, Akin issued more apologies on Monday, saying: “This weekend I made a mistake. I used the wrong words in the wrong way. What I said was ill-conceived and it was wrong and for that I apologize.”

In an unplanned appearance, President Obama used his first news conference in months to pounce on Akin’s remarks.

“Rape is rape, and the idea that we should be parsing and qualifying and slicing what types of rape we are talking about doesn’t make sense to the American people and certainly doesn’t make sense to me,” Obama said. “So what I think these comments do underscore is why we shouldn’t have a bunch of politicians, a majority of whom are men, making health-care decisions on behalf of women.”

Democrats tried to link Akin’s positions on abortion to Rep. Paul Ryan (R-Wis.), the Republican vice-presidential standard-bearer, and other GOP candidates for their co-sponsorship of a 2011 bill that would have strengthened federal prohibitions on abortion funding, redefining rape so that only “forcible rape” would be exempt from the restriction.

Republican strategists, publicly and privately, said Akin’s remarks hit such a raw emotional nerve that his candidacy was effectively over. They said that Akin’s suggestion was both scientifically absurd and politically inept and that forcing a woman to bear a child resulting from a rape was too appalling for many people.

“This comment is indefensible, and it’s going to be very hard to sustain an adequate defense in the face of the avalanche of responses from Democrats and Republicans alike on the national and local level,” said Ron Bonjean, a former top aide to Senate GOP leadership.

Other Senate Republicans and GOP nominees in competitive races were encouraged to release statements condemning Akin’s views in personal terms.

“As a husband and father of two young women, I found Todd Akin’s comments about women and rape outrageous, inappropriate and wrong,” said Sen. Scott Brown (R-Mass.). “There is no place in our public discourse for this type of offensive thinking. Not only should he apologize, but I believe Rep. Akin’s statement was so far out of bounds that he should resign the nomination.”

Cornyn, chairman of the National Republican Senatorial Committee, informed Akin that the national GOP will not spend money to help elect him, according to a committee aide, and Cornyn told him that he is endangering Republicans’ hopes of retaking the majority in the Senate, the aide said.

Republican leaders cannot force Akin to quit, and Missouri has one of the clearest, strictest laws in the nation regarding replacing candidates. Akin has until the end of Tuesday to freely step aside, in which case state Republican leaders would select a replacement. After that, he has until Sept. 25 to petition a court to be removed from the ballot. After Sept. 25, Missouri candidate names remain on the ballot, even in the event of death.

Senate Republicans, needing four seats to claim the majority — or three if Romney defeats Obama — have long viewed McCaskill as the most vulnerable Democrat running for reelection. Missouri has increasingly tilted away from Democrats since her 2006 victory. In the days leading up to Akin’s Aug. 7 primary victory, GOP strategists issued memos claiming that any of the three contenders would defeat McCaskill, but senior advisers made it clear they preferred either of the two alternatives to Akin: John Brunner, a businessman who had the support of the U.S. Chamber of Commerce, and Sarah Steelman, a former state treasurer backed by Sarah Palin.

Akin, a longtime hero to the antiabortion movement, surged to victory behind endorsements from Christian evangelicals such as Huckabee, claiming the nomination with a plurality of 36 percent. His views on abortion — which he later renounced on the Huckabee show — hail from a small wing of the antiabortion movement that says that, during a rape, the trauma sets in motion biological blocks so a woman cannot conceive a child.

A host of leading conservatives said Akin should quit the race, including radio hosts Hannity and Hugh Hewitt and the editorial boards of the National Review and the Wall Street Journal.

A few social-conservative leaders, including Phyllis Schlafly, defended Akin and called on GOP leaders to stop criticizing him.

“They’re making a big thing about an unfortunate remark,” Schlafly said in Tampa as Republicans began debating the GOP platform, including the party position on abortion.

Others, such as Huckabee, took a neutral stance.

The Akin controversy has turned the Senate race in Missouri upside down, but national Republican leaders are most concerned about the issue seeping into the presidential race and other congressional races. A Washington Post-Kaiser Family Foundation poll conducted July 25 to Aug. 5 shows that 55 percent of Americans said abortion should be legal in all or most cases, compared with 42 percent who said it should be illegal. About 17 percent of Americans say abortion should be illegal in all cases, according to the poll.

Ever since the Republican presidential primary contest in January took a turn toward social issues, GOP strategists have feared that the traditional Democratic edge among female voters could grow so large this fall that it could prove insurmountable for Romney. The most recent Washington Post-ABC News poll shows Obama leads Romney in favorability by 22 points among women.

Aaron Blake and Peyton Craighill in Washington and Rosalind S. Helderman in Tampa contributed to this report.