JEFFERSON CITY, Mo. » Rep. Todd Akin defied the nation’s top Republicans today to forge ahead with his besieged Senate campaign, declaring that GOP leaders were overreacting by abandoning him because of comments that women’s bodies can prevent pregnancies in cases of "legitimate rape."

Akin pledged to carry on with his quest to unseat Democrat Claire McCaskill. But his bid faced tall obstacles: a lack of money, a lack of party support and no assurance that his apologies would be enough to heal a self-inflicted political wound.

"I misspoke one word in one sentence on one day, and all of a sudden, overnight, everybody decides, ‘Well, Akin can’t possibly win,’" he said on a national radio show hosted by former Republican presidential candidate Mike Huckabee. "Well, I don’t agree with that."

Akin predicted he would bounce back from the political crisis threatening his campaign and capture a seat that is pivotal to Republican hopes of regaining control of the Senate.

"I’m in this race for the long haul, and we’re going to win it," he told radio host Dana Loesch in St. Louis.

If he stays on the ballot, Akin will have to rebuild without any money from the national party and with new misgivings among rank-and-file Republican voters who just two weeks ago propelled him to a comfortable victory in a hotly contested three-way primary.

At several points during the interview with Huckabee, Akin focused on the idea he had misplaced a single word during a Sunday interview with St. Louis television station KTVI. But Akin has been roundly criticized both for using the phrase "legitimate rape" and saying a woman’s body has the ability to prevent conception after such an attack.

Hours earlier, Akin posted an online video in which he apologized again for his remarks. Campaign spokesman Ryan Hite said the apology was intended to cover both the reference to "legitimate rape" and Akin’s assertion that rape victims have a natural defense against pregnancy.

In a potential sign of his strategy, Akin appealed to Christian evangelicals, anti-abortion activists and anti-establishment Republicans. He said he remains the best messenger to highlight respect for life and liberty that he contends are crumbling under the big-government policies of President Barack Obama.

As a key deadline to withdraw from the ballot loomed, Republican leaders intensified their pressure on Akin to exit.

Sen. Roy Blunt issued a joint statement Tuesday with all four of Missouri’s living former Republican senators — John Ashcroft, Kit Bond, Jim Talent and John Danforth — saying "it serves the national interest" for Akin to step aside.

Pointing to the group, Republican presidential candidate Mitt Romney said the congressman should "accept their counsel."

A Romney aide said the candidate had been inclined to let Akin make the decision on his own. But after the Missouri lawmakers called for Akin to go, Romney wanted to make his position clear, said the aide, who requested anonymity because the aide was not authorized to publicly discuss Romney’s thinking.

The deadline passed without any paperwork from the increasingly isolated Akin.

He provoked a political uproar when he was asked in the KTVI interview whether his general opposition to abortion extends to women who have been raped.

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

In the apology video posted today on YouTube, Akin acknowledged that rape can lead to pregnancy, adding: "The mistake I made was in the words I said, not in the heart I hold. I ask for your forgiveness."

The video will be running as a 30-second ad on TV stations statewide for several days, Hite said.

But it’s not clear if Akin’s campaign will have the financial support to wage a prolonged advertising battle against McCaskill in the expensive St. Louis and Kansas City markets and the Republican-rich area of southwest Missouri.

The campaign arm of the Senate Republicans has already withdrawn $5 million in advertising planned for the Missouri race. The Karl Rove-backed Crossroads organization pulled its ads, too.

Crossroads President and CEO Steven Law suggested Tuesday that Akin was potentially helping Democrats retain their Senate majority by remaining in the race.

"The stakes in this election are far bigger than any one individual," said Brian Walsh, a spokesman for the National Republican Senatorial Campaign Committee. By staying in the race, Akin "is putting at great risk many of the issues that he and others in the Republican Party are fighting for."

While repeating his apology, Akin began taking a more aggressive tone today.

Asked by Huckabee if Akin felt betrayed by fellow Republicans, Akin replied: "I hadn’t done anything morally or ethically wrong, as sometimes people in politics do … It does seem like a little bit of an overreaction."

To continue his campaign, Akin will need the support of social conservatives, who have formed his political base through a 12-year congressional career.

Noreen McCann, who lives in the same suburban St. Louis area as Akin, said Tuesday that his rape comment hasn’t weakened her support for him. McCann expressed frustration that Akin was being publicly flayed for his ill-chosen words while other Democrats — specifically President Bill Clinton — have survived scandals that included accusations of sexual impropriety and lies.

Akin "is a man of principle. I trust and respect his integrity and his commitment to defending American values," said McCann, who had passed out Akin fliers on primary election day. "I think he wants to defend all innocent human life. If he misspoke, or it was in the wrong context, that is not a major problem for me."

If Akin were to leave, state law gives the Republican state committee two weeks to name a replacement. Akin can withdraw from the race as late as Sept. 25, but after Tuesday, he would need a court order to do so.

Associated Press writers Jim Salter in St. Louis and Henry C. Jackson in Washington contributed to this report.