WASHINGTON -- U.S. Capitol Police are investigating a reported threat against Rep. Todd Akin, the Missouri congressman who has been criticized for comments he made recently about rape.
There is "an active, open investigation, Lt. Kimberly Schneider said, without revealing further details, citing a policy against discussing the security of members of Congress.
He has apologized repeatedly and has said he misspoke, and has refused demands by top Republicans that he withdraw from the Senate race.
"I'm in this race for the long haul and we're going to win it," Akin told conservative radio host Dana Loesch.
He spoke minutes after five past and present Republican senators from Missouri, including highly regarded figures John Danforth and Christopher "Kit" Bond, added their voices to widespread calls for Akin to end his campaign.
"We do not believe it serves the national interest for Congressman Todd Akin to stay in this race," said the statement by Sen. Roy Blunt and former senators Danforth, Bond, John Ashcroft and Jim Talent. "The issues at stake are too big, and this election is simply too important. The right decision is to step aside."
Republican presidential candidate Mitt Romney also advised Akin to end his campaign, saying: "His fellow Missourians urged him to step aside, and I think he should accept their counsel and exit the Senate race."
Romney's running mate, Rep. Paul Ryan of Wisconsin, echoed the call, according to a statement from his spokesman.
Other prominent Republicans to join the chorus urging Akin's withdrawal included Wisconsin Gov. Scott Walker and veteran Sen. Kay Bailey Hutchison of Texas.
Akin complained his detractors overreacted to a liberal media campaign to take him down. He said fellow Republicans "ran for cover at the first sound of gunfire."
His decision means he faces the first statewide race of his career with no mainstream GOP backing. After he announced his intention to stay in the race, the National Republican Senatorial Committee made clear it would not provide any help.
A six-term congressman who won more than 60% support in his five re-election efforts, Akin is a staunch conservative Christian who opposes abortion. By staying in the race, Akin's candidacy ensures the abortion issue will be a focal point of next week's Republican National Convention.
Romney is basing his presidential election campaign on economic issues, and the attention to social issues such as abortion distracts from his message that he is better qualified than President Barack Obama to restore strong growth and create jobs.
The GOP party platform being drafted ahead of next week's convention includes an endorsement of a "human life amendment" to the Constitution that would outlaw abortion with no explicit exemption for rape or incest.
The language, approved by the platform committee on Tuesday, is similar to the platforms that were adopted by the party at its conventions in 2000, 2004 and 2008. Convention delegates are expected to approve the platform next week.
The issue is particularly sensitive for Romney's running mate, Ryan, who is a devout Catholic opposed to abortion. The Romney campaign acknowledged that Ryan personally opposes abortion in cases of rape, but said Romney's view is the policy of the ticket.
"Rape is an evil act; I used the wrong words in the wrong way. And for that, I apologize," he said in the new ad that came out Tuesday. "As the father of two daughters, I want tough justice for predators, have a compassionate heart for the victims of sexual assault, and I pray for them. Fact is, rape could 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."
Akin also characterized his mistake as isolated and relatively minor.
"Well it just seems that I just misspoke one word in one sentence on one day," he told Huckabee. "I hadn't done anything that was morally or ethically wrong, as sometimes people in politics do. ... It does seem like a little bit of an overreaction."