Well, all I can tell you is what happened.
I think what may be part of the problem is that, reading it back, it sounds like they were there all day doing it. But they weren't. They challenged voters in the line at the time. It happened about three times during the day. The poll watchers would come in, get sworn in, use signature cards to check lists against their list of voters they had, then would challenge some voters as they came through. (Yes, about 40% of the line, of course that sounds like a ton, but remember that the entire county has less people in it than most small cities, it was only one precinct, most voters use mail in ballots about 65% in fact.)
Seriously, the story sounded a ton more awful when I read it back than what I meant it to sound. All in all, about 30 voters were challenged that day.