There are two types of activities known as ballot harvesting. One is perfectly legal and beneficial to society. That is when someone helps the voter get their absentee ballot and/or helps them return it properly. Perfectly valid for situations like when someone is in a hospital, nursing home, etc., or even to help them comply with the rather rigid rules on absentee ballots. If that is what Nunes is talking about, that's fine. It's legal in my state under very strict guidelines.
The other way of harvesting-highly illegal-is when you apply and vote for absentee ballots for other people, or collect completed absentee ballots and only submit those that will favor your outcome, etc. Here's a summary of this sort of election fraud-done by a GOP operative:
How Republicans Tried to Rig an Election in North Carolina (And Almost Got Away With It)
It’s been nine months, and the district still doesn’t have a congressional representative. But voters head to the polls again soon.
www.gq.com