Michele Bachmann says the HPV vaccine is dangerous? Fact-checked.

Mitt Romney claims to have created 100,000 jobs in private-equity racket? Fact-checked.

Rick Perry claims expertise on Mitt Romney’s book? Fact-checked.

Gary Johnson unfamously says, “We’re bankrupt.”? Fact-checked, believe it or not.

Newt Gingrich declares “false” his ex-wife’s claims that he requested an “open marriage”? Uh. Um. Well.

Here’s a big-headline factual dispute. Either you believe Newt Gingrich — that he didn’t request an open marriage — or you believe Marianne Gingrich — that he did request such a thing. Isn’t that just the kind of dispute that fact-checkers can resolve?

No way.

Glenn Kessler mans the fact-checking station here at The Washington Post. Late last night, he vetted a mountain of factual contentions that got thrown around in the Charleston, S.C., debate. Not among them was the open-marriage thing. Why’s that? Kessler writes:

This is a classic case of he said, she said. It would be difficult to get to the bottom of it, especially because memories fade or change over time. We also don’t know the context in which this alleged statement was made. Gingrich might be able to produce friends — though who imagines telling a friend that you did not discuss open marriage — but she might produce friends with whom she discussed the alleged conversation. The best source of information would be the divorce records, and especially any statements made under oath at the time. Then memories would be fresh and people presumably would be compelled to tell the truth., which has won the Pulitzer Prize for its work in exposing truth, homes in on various lines from last night’s tilt, including claims about taxpayer-funded abortions, the popularity of health-care reform in Massachusetts, among others. And nothing on open marriage.

Says PolitiFact’s Bill Adair via e-mail, “This probably isn’t one that we could do a Truth-O-Meter rating on because it would be difficult to get enough certainty to rate it True or False. But other journalists can still use traditional techniques to explore it by seeking corroborating evidence from both sides.”

Good luck to those “other journalists.” Though Gingrich said in last night’s debate that his camp offered sources to ABC to counter Marianne Gingrich’s version of history, ABC has a different recollection: “That’s just not true,” says Senior Vice President Jeffrey W. Schneider.

Here’s another consideration that tells fact-checkers they’re not welcome in this story: In this account, Marianne Gingrich reports that when Newt Gingrich requested this now-famous “open marriage,” he didn’t use that term. Rather, the term is an abridgement of whatever he requested of Marianne Gingrich. Meaning that this territory is marked by spongy, squishy marshland — no place for people like Kessler and Adair. If only Marianne and Newt were fighting about prescription-drug benefits!