In the first season (or 2nd)? didn't the judges bring some contestant back that was voted off? For some reason I think they did that - does anyone else remember this? If so I would think they'd bring back Constantine.
No not to the competition. When they were trying to pick the final 12 they brought back a group of 10 who had not been voted on for the finals. Amazingly enough Clay Aiken was in this group because Kimberly was voted for over him. Once the final 10-12 are chosen though that is it. No one is brought back unless a contestant quits or is removed. Then they do like they did with Nikko and bring back the one that has the 2nd most votes.
In the first season, AI had finally sifted down to the TOP TEN when it was discovered that one contestant (can't remember the name) had lied about his age. The limit back then was 24 or 25 and this guy was 29. So they booted him and brought back semi-finalist E.J. Day. He could barely sing, though, and was voted off the first night of the finals.
In season 2 (and maybe 3), the judges had a "second chance" group perform again in the semi-finals. This group consisted of people that the judges thought deserved another shot. Clay Aiken was in this group. He won and went on to the Top Twelve.
And this season, Nikko Smith was brought back to replace Mario Vazquez.