What happened?
Swalwell presented a tweet from a Trump follower that Trump re-tweeted. The impeachment managers changed Jen Lawrence to be a verified Twitter user (blue check). She was never a verified Twitter user. Swalwell confused Calvery, in the biblical sense, to cavalry as in fighters on horseback. He completely misrepresent the Jen Lawrence tweets.
I think that is what the Trump lawyers referred to when saying in Philly, if you are caught doctoring evidence, your case is over.