What‘s driving Bachmann’s gaffes?

Michele Bachmann appears to have a strong penchant for saying the un-sayable (possibly un-backable), but with such sincerity you can only assume she means every word. How come?

The New York Times published an article Thursday that might have some clues:

People close to the campaign, who spoke on condition of anonymity, said Mrs. Bachmann is often influenced by the last person she speaks with on an issue rather than maintaining discipline in communicating a message.

She made the link between the vaccine and mental illness after meeting a tearful woman following Monday night’s debate, she said. The woman said her daughter had developed mental retardation after being vaccinated against human papillomavirus, which can cause cervical cancer.

Mrs. Bachmann repeated the account Monday night on Fox News and the next morning on NBC’s “Today,” warning that Mr. Perry’s executive order in Texas would have forced young girls to receive “an injection of what could potentially be a very dangerous drug.”

[...]

In some cases, campaign insiders said, Mrs. Bachmann’s staff was to blame for feeding her misinformation — such as that New Hampshire, rather than Massachusetts, was the site of “the shot heard round the world” that began the American Revolution, which she told a crowd in Manchester, N.H., in March.

In regards to her vaccine-retardation claim, Bachmann said Thursday in her defense, "During the debate, I didn’t make any statements that would indicate that I’m a doctor, I’m a scientist or that I’m making any conclusions about the drug one way or another,” according to CBS News.

There's no strong indication yet as to whether Bachmann's gaffes, many of which she has made before entering the presidential race, will cost her in the primary. She won the Iowa straw poll in early August and still polls within the top four Republican candidates in terms of favorability, according to Gallup.