For the second straight day, Akin appeared on former Arkansas Gov. Mike Huckabee's radio show to say he will remain in the race against incumbent Democrat Claire McCaskill despite pressure from GOP leaders -- including presumptive presidential nominee Mitt Romney -- to leave the race because of his remarks Sunday about "legitimate rape" and the odds of conception.
Akin had faced a 6 p.m. EDT deadline to withdraw so his name could be removed easily from the ballot failed. The Missouri Secretary of State's office said the deadline came and went without action by Akin, the St. Louis Post-Dispatch reported.
"There's an active and engaged and committed grassroots movement," the newspaper quoted Akin as saying on Huckabee's radio show. "We believe by taking this stand we can strengthen this country."
"We do not believe it serves the national interest for Congressman Todd Akin to stay in this race," they said in a joint statement. "The issues at stake are too big, and this election is simply too important. The right decision is to step aside."
Romney Tuesday repeated his observation that 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 recorded a TV ad acknowledging he used "the wrong words in the wrong way" concerning rape and pregnancy.
In the ad, previewed Tuesday by Politico, Akin said: "Rape is an evil act. I used the wrong words in the wrong way and for that I apologize. As the father of two daughters, I want tough justice for predators. I have a compassionate heart for the victims of sexual assault. 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.
U.S. Sen. Patty Murray, D-Wash., who heads the Democratic Senate Campaign Committee, released a statement accusing Republicans who were pressuring Akin to leave the race of "faux outrage"
"This is not about principle," Murray said. "Congressman Akin's substantive position on choice is the official position of the Republican party. This is about Washington Republicans playing politics with the voters of Missouri, plain and simple."
Murray said Republican reaction to Akin's comments was "hypocrisy of the highest order."
"No one in the Republican establishment is standing up today to protest the party platform, which forces rape victims to carry their pregnancy to term. If Washington Republicans are not willing to stand up and defend rape victims when it counts, they should not have a say when Missouri Republicans nominate a candidate who shares that view."
Akin has come under heavy criticism from Democrats, women and members of his own party for his comments Sunday when asked if abortion should be legal in the case of rape.
"From what I understand from doctors, that's really rare," Akin said during the interview with a St. Louis television station. "If it's a legitimate rape, the female body has ways to try to shut that whole thing down."
The controversy prompted the National Republican Senatorial Committee to say it would pull the $5 million it planned to spend on the Missouri race unless Akin quits. Crossroads GPS -- a conservative political action committee operated by Fox News commentator and former White House adviser Karl Rove -- said it was withdrawing ads scheduled to start Wednesday in Missouri.
"It's a devastating problem to have that not only are Republicans walking away but the advertising money is, too," Republican strategist Ron Bonjean told Politico. "If you're an army fighting a battle and you've lost your air cover, it's likely you're going to have a hard time winning a war."
Missouri voters strongly disagree with Akin's comments, but a Public Policy Poll indicates he leads McCaskill 44 percent to 43 percent, showing little movement in the campaign since May.
Seventy-five percent of Missouri voters, including 64 percent of Republicans, said the comments were inappropriate while 9 percent said they thought they were appropriate, results indicated. Seventy-nine percent of voters say they disagree with what Akin said.
Twenty-four percent of voters said they have a favorable opinion of him to 58 percent with a negative one, PPP said.
Results are based on telephone interviews of 500 likely Missouri voters Aug. 20. The margin of error for the survey is 4.4 percentage points.
Under Missouri law, if a candidate leaves the ballot 11 weeks before Election Day, the Missouri Republican central committee would have two weeks to choose a replacement for the November ballot.
Akin can wait to quit until anytime before Sept. 25 -- six weeks before the election -- but his withdrawal at that time could be challenged by Missouri Secretary of State Robin Carnahan, a Democrat, The New York Times said.