Everything they did was legal.
O'Keefe Voter Fraud Investigation: Young Man Offered Holder's Ballot
"The video shows a young man entering a Washington, DC polling place at 3401 Nebraska Avenue, NW, on primary day of this year--April 3, 2012--and giving Holder’s name and address. The poll worker promptly offers the*young man Holder’s ballot to vote.*
The young man then suggests that he should show his ID; the poll worker, in compliance with DC law, states: “You don’t need it. It’s all right. As long as you’re in here, you’re on our list, and that’s who you say you are, you’re okay.”*"