If you ever discuss politics on social media and your friend-o-sphere has any partisan diversity at all, undoubtedly you've run into this tactic: You're in a discussion about some Trump outrage — favoring Putin's interests over America's, seizing the children of immigrants making a legal application for asylum, "draining the swamp" by asking us to stomach conflicts of interest an a scale previously unknown in American history, or one of the many others — when somebody comes out with "Yeah, but what about …" and then refers to some right-wing conspiracy theory you've never heard before about Obama, the Clintons, George Soros, the Mueller investigation, or something else.
It takes maybe five minutes to find whatever-it-is on Snopes, and maybe another ten (if you're trying to be conscientious and not just rejecting unwelcome theories out of hand) to satisfy yourself that it really is a piece of baseless nonsense. 
And then what do you do?
If you just move on, no one else benefits from the research you've done, and other readers of the thread might think the point actually has some validity. (Although probably not. People who do this once have probably done it dozens of times, and their friends have caught on by now.) But if you respond, then the Trumpist comes back with three more ridiculous claims — the sources you've relied on are all part of the Deep State conspiracy, the Sandy Hook parents are really crisis actors, and you've ignored the implications of PizzaGate completely — and now you're in a full-blown argument that has nothing to do with Trump at all. In fact, it has nothing to do with anything, because the whole discussion has veered off into CrazyLand.
And that was the point, wasn't it? The person you're arguing with actually doesn't care about Andrew McCabe's wife's run for the legislature or Lisa Page's text messages or how Vince Foster died or whatever else you're now talking about. Once there was a discussion about something indefensible Trump was doing, and now there's a discussion about bullshit. Mission accomplished!
This tactic is sometimes called Whataboutism, but that's actually a more general term. The Whataboutist is also trying to divert your attention from an uncomfortable present issue onto some tangentially related issue, but there's a difference: The Whataboutist's new topic might actually be related and might actually be an issue.
So if you're talking about Trump's abuse of women and a Whataboutist brings up Bill Clinton, that's probably also a bad-faith attempt to change the subject — it's hard to see why Clinton stories that have been around since the 1990s are more topical than the long series of Trump stories that started coming out after the Access Hollywood tape appeared and may not be done yet — but at least it's real: There actually was a Monica Lewinsky scandal, even if it has nothing to do with anything today.  Similarly, if you're complaining about how the Trump tax cut blows up the deficit and someone tries to change the subject to the even-larger deficits of Obama's first couple of years, that's not just a true fact that a thoughtful person might actually wonder about, there's even something important to understand about it. (Deficits intended to pull the economy out of a deep recession can be economically responsible. Deficits intended to keep an expansion going past its sell-by date never are.)
But when the topic you get derailed onto has no basis in reality, that trick deserves its own term, and I recently ran across one: Bullshifting. 
Bullshifting is a conversational judo move that uses your own outrage against you. Precisely because the suggested topic is so stupid and such a complete waste of your time, it's hard not to respond. The Bullshifter is mimicking exactly the behavior you have probably fantasized about attacking. He or she is like a bird that pretends to be wounded to draw a predator away from its nest. "I'm so gullible," s/he seems to be announcing. "I'm such a mindless drone for Alex Jones. I repeat every ridiculous thing Sean Hannity says. Come humiliate me in front of everybody."
But the predator never catches the bird with the fake-broken wing, and you never successfully humiliate the Bullshifter either. Because Bullshifters argue in bad faith, they can make up whatever facts are necessary to wriggle out of any refutation you come up with. (In a good-faith argument, you can eventually reach mutual agreement on some kind of ground truth that future deductions can build on: Water is wet; granite is heavy. But bad-faith arguments are bottomless.) All that happens is that you get drawn farther and farther away from your original valid point. 
So what is the proper response to Bullshifting? When the culprits are people that the rest of your social media universe will recognize as wingnuts without your help, you should just ignore them, as hard as that is. If you feel that you must engage, I recommend that you label the comment rather than respond to it: "Nice attempt to bullshift. But my original point stands: [restate]."
If they respond by raging at you, repeat the loop: Can you ignore? If you can, do. If not, call bullshift and restate.
The first few times you do this, you may need to educate your social-media friends by posting a link to this article or some other explanation of the concept. If you're lucky, the Bullshifter will leave a nasty comment here rather than on your Facebook wall. You will have successful shifted the shifter.
No need to thank me. It's a public service of The Weekly Sift.
 This is an example of Brandolini's Law: "The amount of energy needed to refute bullshit is an order of magnitude bigger than to produce it."
 When Hillary was running for president, Whataboutists could make some triple-bank-shot argument about why Bill's misdeeds were relevant. But now that both of the Clintons are private citizens and likely to remain so, there's really no reason to ever discuss Monica again.
 I would credit the coiner if I could determine who it is. If you google it, you'll find that bullshift also has several other meanings — that's why I'm having trouble tracking down the origin of this usage — but they're sufficiently different to avoid confusion.
This meaning of bullshifting derives from the technical meaning of bullshitting, as described in 1986 by Princeton philosopher Harry Frankfurt in his seminal paper "On Bullshit" (which was later expanded into a book).
When an honest man speaks, he says only what he believes to be true; and for the liar, it is correspondingly indispensable that he considers his statements to be false. For the bullshitter, however, all these bets are off: he is neither on the side of the true nor on the side of the false. His eye is not on the facts at all, as the eyes of the honest man and of the liar are, except insofar as they may be pertinent to his interest in getting away with what he says. He does not care whether the things he says describe reality correctly. He just picks them out, or makes them up, to suit his purpose.
So when a used car salesman tells you how conscientiously a car's former owner maintained it, he is probably bullshitting rather than lying. Quite likely he has no idea what the truth of the matter is and doesn't care. He just wants to sell you the car.
Donald Trump is the quintessential bullshitter. He described an instance of his own bullshitting at a fundraiser in March:
[Canadian Prime Minister] Trudeau came to see me. He's a good guy, Justin. He said, "No, no, we have no trade deficit with you, we have none. Donald, please." Nice guy, good-looking guy, comes in — "Donald, we have no trade deficit." He's very proud because everybody else, you know, we're getting killed. … So, he's proud. I said, "Wrong, Justin, you do." I didn't even know. … I had no idea. I just said, "You're wrong."
There's been a lot of discussion in the media about when to label a false Trump statement as a "lie" rather than to use "demonstrable falsehood" or some other euphemism, none of which seem quite right. The problem is that the most precise characterization of the majority of Trump's false statements — as well as his true statements and almost every assertion that comes out of his mouth — is "bullshit", a word that most mainstream publications would rather not use.
 Unsurprisingly, the champion Bullshifter is Trump himself. In Helsinki, when he was asked whether he believed American intelligence services (headed by people he appointed himself) or Vladimir Putin, Trump first had to veer off into the "mystery" of the missing DNC server. (As The Daily Beast's Kevin Poulsen explains, "Trump's 'Missing DNC Server' is Neither Missing Nor a Server".) Anybody who tries to cover his answer conscientiously first has to wade through the bullshit, which was why Trump spread it in the first place.