For a network that dedicates so much effort to tracking and cautioning against the spread of online misinformation, you would think that MSNBC would be more careful with what its guests and hosts say on air.

But you would be wrong! The fake news is coming from inside the house!

MSNBC contributor Joy Vance thought it would be a very funny thing this weekend to claim that Fox News plans to boycott special counsel Robert Mueller’s Wednesday testimony before Congress. None of this is true, of course. Fox News is covering the Mueller hearings. Vance’s claim is pure fiction.

“Fox isn’t showing Mueller’s testimony Wednesday,” she tweeted. “Trump is afraid of what will happen if his base gets to hear Mueller’s testimony for themselves.”

Vance deleted the note later, claiming that it was a joke that got away from her. I am not sure where the joke is. Jokes normally have some sort of set up and payoff, neither of which are present in Vance's since-deleted tweet. But OK. Whatever she says.

“Y’all, a kind friend pointed out my goofy sense of humor doesn’t always translate onto Twitter. I know most of you get the irony by now. It will be interesting to see Fox’s coverage in light of Trump’s statement he won’t be watching the hearing,” she said.

Vance added, “I’ve deleted an earlier tweet I intended ironically, but that some took as factual regarding Fox news coverage of Mueller’s testimony. My apologies to anyone I confused. I don’t like to delete tweets but that seems a better course than unintentionally misinforming people.”

Unfortunately, no amount of clarification can undo the initial lie. We have seen this a hundred times: A mistaken or dishonest individual pushes a falsehood, it appeals to the ingrained biases of rabid partisans, and the next thing you know you have an indestructible narrative based entirely on a fabrication. Vance’s attempt this weekend to walk back her alleged joke has done little to halt the spread of her original and very persistent lie. The lie is so persistent, in fact, that it has been repeated on at least two separate occasions on MSNBC’s own programming.

“Fox News … is not airing the Mueller testimony live,” former Rep. Donna Edwards, a Democrat from Maryland, claimed Tuesday morning.

Earlier, on Monday, MSNBC contributor Rick Wilson also claimed Fox did not plan to show Mueller’s testimony.

“Fox isn’t covering the hearings, which should also tell you how scared they are of what could happen on this morning,” he said. “It’s going to be a very interesting and consequential moment. They’re apparently not going to take them live. Everybody else is taking them live.”

His host, Nicolle Wallace, gasped, “Really?”

No. Not really.

Anyway, I cannot wait for the next round of anxious MSNBC reporting on the disastrous effects of online conspiracies and hoaxes. It should be enlightening.