What is the term for repeating something in an A, B, A fashion? (e.g. "Just the facts, ma'am, just the facts.")

It is called "diacope"

Diacope is a rhetorical term meaning repetition of a word or phrase with one or two intervening words. It derives from a Greek word meaning "cut in two".

"Put out the light, and then put out the light."–Shakespeare, Othello, Act V, scene 2.

Further explanation:

• For maximum effect, there should not be too many words between the repeated word(s) in a diacope.

• Diacope is similar to epanalepsis. In the latter, the repeated words are at the beginning and end of a sentence. The last quote, by Denzel Washington, is both a diacope and epanalepsis.

“Don’t turn away from the truth. Don’t turn away from your conscience. Please don’t ignore the law; no, embrace that higher principle for which the law was meant to serve. Justice—that’s all I ask—justice.”

— Denzel Washington in The Hurricane (1999)

You already found the word you're looking for: "epanalepsis."

epanalepsis: a repetition of a word or a phrase with intervening words setting off the repetition, sometimes occurring with a phrase used both at the beginning and end of a sentence, as in the immortal words of Jack Webb: "Just the facts, ma'am, just the facts."