Complex sentence: Tanner has been a prominent member of the party's Socialist Left faction and it was thought that he might contest the Labor leadership in 2002, when Kim Beazley first challenged Simon Crean.
Split into simpler sentences: Tanner has been a prominent member of the party's Socialist Left faction. It was thought that he may join in the leadership spill in 2002, when Kim Beazley first challenged Simon Crean.