On Thursday, he said: "I don't want her to get away with this on the 24-hour news cycle. Somebody ought to hold her accountable."
Actually, a Caplan colleague had already tried to do so.
Steven Miles, a bioethicist at the University of Minnesota Medical School - where Caplan used to be his boss - on Tuesday used Facebook to offer $1,000 for "a properly signed medical release" verifying Bachmann's assertion.
On Thursday, Bachmann's press secretary, Alice Stewart, said she couldn't comment on Caplan's reward offer because she hadn't seen it.
She also said Bachmann's initial vaccine comments, made Monday during a debate with other GOP presidential candidates, were a criticism of Rick Perry. As Texas governor, Perry had signed an executive order - later overturned by the Legislature - mandating that 12-year-old girls receive the vaccine, which protects against the virus that causes cervical cancer. It is made by Merck & Co. at its vaccine plant in West Point, Pa.
"The point she was making was the fact that Gov. Perry exceeded his executive privilege," Stewart said. "He bypassed the legislative process."
But Bachmann also cast aspersions on the vaccine.
"Little girls who have a negative reaction to this potentially dangerous drug don't get a mulligan," Bachmann proclaimed during the debate. "They don't get a do-over. The parents don't get a do-over."
In post-debate interviews, she elaborated with the "retardation" anecdote.
Of the 35 million doses of Gardasil distributed in the United States as of June, not one resulted in a report of mental retardation, according to the U.S. Centers for Disease Control and Prevention. About 92 percent of the 18,728 reports of side effects involved minor problems such as headache, soreness at the injection site, or nausea. Serious adverse events - not proven to be related to the shots - include the neurological disorder Guillain-Barré syndrome, blood clots, and death.
Some have speculated that Bachmann was trying to play on unfounded fears that childhood vaccines are linked to autism. British scientist Andrew Wakefield posited that link more than a decade ago in a study later shown to be fraudulent.
"We've worked hard to get rid of the words mental retardation. We prefer intellectual disabilities," said Curt Decker, executive director of the National Disability Rights Network in Washington. "If she's going to try to raise the specter of some other disability such as autism, it's just taking the conversation in the absolute wrong direction."
Bachmann has made more than a few misstatements, as Internet video clips can attest.
Last week, she called emergency contraception "the morning-after abortion pill," even though the tablets contain the same hormones as birth control pills and cannot disrupt an established pregnancy.
Bachmann has also confused the birthplace of serial killer John Wayne Gacy with that of movie star John Wayne; implied that the former Soviet Union not only still exists but is a rising superpower; portrayed the Revolutionary War as starting in Concord, N.H., rather than Lexington and Concord, Mass.; and claimed that the "Founding Fathers" ended slavery (George Washington and Thomas Jefferson owned slaves).
Unlike these missteps, her comments about the cervical cancer vaccine could do real harm, said Miles, the Minnesota bioethicist.
"The claim is a very serious one because it has the potential to cause people to make health-care decisions," he said.
He noted that in recent months, Minneapolis has had dozens of cases of measles among unvaccinated children. Some of their parents met last spring with a guest visitor - Andrew Wakefield.
"A 3-year-old with measles is on life support," Miles said.
Contact staff writer Marie McCullough at 215-854-2720 or email@example.com