The code used is the Perjury code, the tactic is to bring up something from years ago, don't allow the person access to what they said, and ask them again as part of a deposition. Any deviance, even due to honestly forgetting about the past occurrence, is now Perjury.
The best part is the whole exercise isn't to get a conviction, but to just the the CHARGE out and make the person defend themselves, giving the press opportunities to dig further and find unrelated dirt on the person.
It is the fruition of the left's desire to destroy anyone opposing them.