There's no doubt that the companies have been taking at least some steps to boot extremists from their platforms, such as AI algorithms and more aggressive content bans. Congress' worry, as you might guess, is that tech firms could be doing better -- that propaganda is slipping through the cracks at an unnecessarily high rate.

Whether or not it is, there's a chance that the companies may face pressure to talk about their ability to combat other destructive material, whether it's hate speech, abuse or Russian influence campaigns. They've already discussed some of this before, but they may be put on the spot by senators looking for any area where Facebook, Google and Twitter might fall short.