Complex sentence: Gritz has claimed he accepted the party's nomination with the belief he would be the running mate of James Traficant, and that sometime after learning it would be not be Traficant but Duke and sometime after meeting Duke, he decided to drop out.
Split into simpler sentences: Gritz has claimed he accepted the party's nomination with the belief he would be the running mate of James Traficant. After learning it would be not be Traficant but Duke, he decided to drop out.