It used to be a rarity for Silicon Valley to come to Washington.

Now it’s old hat: Since the fall of 2016, tech leaders have been shuttling back and forth to the U.S. Capitol. Some of the visits are behind-the-scenes talks; some are high-profile public presentations, like the ones Mark Zuckerberg sat through this spring.

So we’ve seen many previews of Wednesday’s pair of hearings, which feature Twitter CEO Jack Dorsey and Facebook COO Sheryl Sandberg appearing before the Senate Intel Committee in the morning, and Dorsey appearing solo at the House Energy and Commerce Committee in the afternoon.

What’s new is the context. While Twitter, Facebook and Google executives have spent much of the last two years defending their companies’ performances during the 2016 election, now they’re under attack for supposedly suppressing conservative voices on their platforms. And the fact that the charges are mostly nonsense doesn’t mean they will go away.

Here’s a quick primer on what’s at stake for Twitter, Facebook and Google during tomorrow’s hearings:

Google: You won’t hear from Alphabet CEO Larry Page or Google CEO Sundar Pichai during tomorrow’s Intel Committee hearing, which upsets the Senators who organized it. Alphabet/Google argues that the exec it wanted to send instead — top lawyer Kent Walker — would do just fine, but committee chairs Sen. Mark Warner and Sen. Richard Burr disagree. So expect them to place an empty chair next to Dorsey and Sandberg during the session, to publicly shame Google for not sending their most high-profile execs. That makes for a lousy picture (here’s what it looked like at Code a few years ago, when Peter Thiel declined to sit and talk with us and Gawker founder Nick Denton) but Google seems to be betting it is better off in the long run. Best-case scenario: Google can’t say something in public it has to regret later. Worst-case scenario: Slighted senators take the snub out on Google down the road.

Facebook: Sandberg, the former chief of staff for Treasury Secretary Larry Summers, knows her way around D.C. More important, she knows her way around a question she doesn’t want to answer directly, and how to turn that question into an opportunity to say something she wants to say. You know how Mark Zuckerberg did just fine answering questions from Congress last spring? Imagine that performance, but smoother.

Facebook, like Google and Twitter, believes it has adequately explained what happened in 2016 and what it is doing to stop a repeat in 2018, but Sandberg will say it again, with a smile. The wild card: The intel committee has theoretically brought Sandberg in to talk about Facebook’s efforts to prevent election meddling from Russia and other bad actors, which she is happy to talk about. What happens if Republican senators, following the lead of Donald Trump and Sen. Orrin Hatch, use the hearing to rail against Facebook for real or imagined anti-conservative bias? Sandberg’s preppers believe that scenario is unlikely, given the makeup of the committee. But they have planned for it anyway.

Twitter: The best-case scenario for Dorsey is a very long day on Capitol Hill. But there are lots of ways for this to go badly for him. Part of this is a matter of seasoning and temperament: Dorsey does some public appearances, but he isn’t a professional talker. And when he does talk, he tends to approach questions with what can scan as a … detached affect. The bigger problem: While Dorsey and Twitter are well-versed in handling questions about election interference, the bias story is a new one, and Dorsey is going to spend an entire afternoon, by himself, handling it, at a session dedicated to “Twitter: Transparency and Accountability.”

Credit Dorsey for showing up for this, because it’s going to be hard. Even in the most controlled setting, Twitter’s bias charges are difficult for Dorsey to swat away — in part because it’s hard to disprove a negative and in part because there is plenty of ammunition for conservatives who want to make bad-faith arguments.

An easy one: Why hasn’t Twitter punished lefties in the same way it has punished far-right-wing Twitter provocateurs like Milo Yiannopoulos, Richard Spencer, Roger Stone and Alex Jones? Twitter’s real answer, if it could speak honestly, is that all of those people have behaved terribly on its platform. The more muted, public one: Well, we did ban award-winning TV writer David Simon a couple times.

Add in Dorsey’s common-sense acknowledgement that Twitter employees have a “left-leaning bias” that they try hard to battle against and this week’s WSJ story reporting that Dorsey weighs in on what to do about high-profile Twitter users accused of bad behavior — which he says is not true — and it’s going to be a rough day.