Luke Joyce, Andy Procter and Sean McConville sealed the victory before the first-half whistle blew, but the Bantams were unable to rally after the break and sit in 19th place with three games remaining.
Jackson said: "We were dreadful, there is no getting away with it. We didn't turn up in the first half.
"It was better in the second half but at half-time the game was lost. The fans were singing 'you're not fit to wear the shirt' and for some of them they were right.
"We need a win and the games are running out as results haven't gone our way. I was disappointed and they`ve let me down. I can see in the fans faces how angry they are and I understand it.
"We`ve got to try and get a win at Aldershot on Monday now. We are in training on Sunday and have to re-group."
Source: PA
Source: PA