Christian (like, Gail Kim) was in TNA from 2005-2009.
While there he had instant success, and quickly beat Jeff Jarrett to become NWA World Heavyweight Champion at 2006 TNA Against All Odds. Also while in TNA, Christian formed Christian's Coalition, along with Tomko and Scott Steiner. They helped him retain his title on numerous occasions.
Once Christian's TNA contract had expired, he re-signed with the WWE in 2009. He became ECW champion, but was drafted to Raw when ECW ended. He did next to nothing on Raw, and was drafted to Smackdown in April in the 2010 WWE Draft. He competed in a tournament to crown the WWE Intercontinental Champion, but lost in the Finals to Kofi Kingston.
That pretty much leads us to where we are now with Christian in the middle of a feud with Drew McIntyre, I think.
I never really understood what happened with Christian's career in WWE. Christian and Edge were the tag team, E&C and along with The Hardyz and The Dudley Boyz, they revolutionized the TLC Match.
So when E&C broke up, Edge went on to become a 9-time World Champion and the biggest thing Christian's done is become ECW champion. Edge and Christian are about the same when it comes to wrestling ability and mic skills, I'd even venture to say that Christian is better.
I think that if WWE does not start utilizing Christian in say a year, then he should jump ship to TNA.
TNA realizes Christian's talent and abilities. He does not have to immediately placed in the main event like so many people have, he can stay in the midcards a little while and then go for the TNA World Heavyweight Title.