When Democrat politicians decide they're going to run with a narrative, it has nothing to do with whether the narrative is true. It only has to do with whether they can sell it. The average person doesn't know the legal definition of perjury. The average person who shares news links on social media doesn't know either. If you repeat it enough and you convince these people that something happened, you've got a shot at winning the perception game and it may as well have happened.
So when they run around suggesting that Jeff Sessions committed perjury in his confirmation hearings, they know he didn't. They don't care. It's not as if the media are going to "fact check" them, because the media are helping to sell the narrative too. The only thing that matters is their ability to sell the narrative to enough of the public.