Updated at 1:20 p.m.

When Rep. Todd Akin (R-Mo.) remarked in a Sunday interview that “legitimate rape” rarely causes pregnancy, Democrats promptly denounced the comment. But for Akin, the larger concern right now might be that Republicans -- both inside and outside of Missouri -- are sharply condemning the GOP Senate nominee's comments, and even calling for him to end his campaign.

Akin on primary night. (Associated Press)

In an interview with National Review published Monday morning, presumptive Republican presidential nominee Mitt Romney offered a sharp rebuke to Akin. “Congressman’s Akin comments on rape are insulting, inexcusable, and, frankly, wrong,” Romney told National Review. “Like millions of other Americans, we found them to be offensive.”

Prominent Senate candidates also weighed in on Monday, with Sens. Scott Brown (R-Mass.) and Ron Johnson (R-Wis.) calling on Akin to resign the nomination for the Senate. Former congresswoman Heather Wilson, the Republican Senate nominee in New Mexico, also called for Akin to end his bid.

“As a husband and father of two young women, I found Todd Akin’s comments about women and rape outrageous, inappropriate and wrong. 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 for US Senate in Missouri," Brown said in a statement.

"Todd Akin’s statements are reprehensible and inexcusable. He should step aside today for the good of the nation," tweeted Johnson. Johnson was a supporter of John Brunner, one of Akin's opponents in the GOP primary.

Rep. Denny Rehberg (R-Mont.), who is running against Democratic Sen. Jon Tester, said he found Akin's comments "to be offensive and reprehensible. There is no such thing as a 'legitimate rape.' I condemn Representative Akin’s statements in the strongest possible terms.”

"I oppose abortion, but exceptions must be made for rape, incest and to protect life of the mother. Cong. Akin's comment was wrong," tweeted Rep. Jeff Flake (R-Ariz.), another GOP Senate candidate.

The chairman of the National Republican Senatorial Committee Chairman, Sen. John Cornyn (R-Texas), said "Akin’s statements were wrong, offensive, and indefensible," and urged him to promptly consider his next move.

"Over the next twenty-four hours, Congressman Akin should carefully consider what is best for him, his family, the Republican Party, and the values that he cares about and has fought for throughout his career in public service," said Cornyn, in a statement.

While Republicans around the country are making it clear they do not agree with Akin, he also has to worry about a lack of support from Republicans in his own home state, many of whom did not share a warm relationship with the congressman, even before his Sunday comments. Akin did not have a reputation as a Republican who would go out of his way to help others in the party with fundraising or other structural support, Missouri Republicans say.

"Don’t expect Missouri Republicans to defend Akin,” said one Missouri-based GOP strategist granted anonymity to speak candidly about the situation. “Akin has never helped fellow Republicans so no one has any loyalty to him."

"Does Akin have broad based support in the party? No he doesn't," added a second Republican operative with experience in Missouri politics.

Sarah Steelman, the former state treasurer who lost to Akin in the GOP primary, tweeted, "Todd Akin's remarks about 'legitimate rape' were inexcusable, insulting and embarrassing to the GOP."

Akin appeared committed to continuing his campaign Monday afternoon, saying in an interview on former Arkansas governor Mike Huckabee's radio show, "No one has called me and said, 'Todd, I think you should drop out.'" Huckabee endorsed Akin in the Senate GOP primary, and appeared in advertisements on his behalf.

Sunday's comments brought Akin more national attention than he has ever received. But it was not the first time he has raised eyebrows with controversial public statements (a reason why Democrats wanted to run against him in the general election, and even boosted his candidacy in the primary). He once said "America has got the equivalent of the stage III cancer of socialism because the federal government is tampering in all kinds of stuff it has no business tampering in." He recently expressed his opposition to federal funding for the National School Lunch Program.

Some Democrats criticized Akin's comments on Monday, and sought to tie his words to the broader GOP.

"Rep. Todd Akin’s comments are reprehensible.  I understand that Scott Brown and other Republicans want to pretend Todd Akin is an isolated individual, but he is clearly in line with the Republican agenda," said Massachusetts Democratic Senate candidate Elizabeth Warren.

"Akin's choice of words isn't the real issue here. The real issue is a Republican party -- led by Mitt Romney and Paul Ryan -- whose policies on women and their health are dangerously wrong," wrote Democratic National Committee Chair Debbie Wasserman Schultz in an email encouraging supporters to sign a petition standing up for women.

Akin's tendency to step in hot water during media interviews means Republicans considering donating money to his campaign moving forward will think twice before writing him a check. And that does not bode well for his chances in November, which are quickly slipping away.

"Everyone is wondering what will be tomorrow, what will he say next? I think that's the biggest problem here," said the Missouri-based GOP strategist.

Akin won the nomination in a three-way primary earlier this month. The only way he does not appear on the ballot in the fall is if he voluntarily steps aside. He can do so by this Tuesday, or by court order (which “shall be freely given” unless the election authority opposes the request and shows good cause) by Sept. 25. The Republican state central committee would select a replacement for Akin, if he steps aside.

The chorus of Republican opposition would be enough to force many politicians out of a race. But Akin has always done things his own way, and that suggests the possibility that he may just stick it out until November. If he does, a state long-considered a strong Republican pickup opportunity might well slip into Democratic hands.