Complex sentence: In 2008 Michael Steele left the RLC, of which he was a founding member of in 1993 citing disagreements over endorsing primary candidates, though some contend that his departure was a politically convenient effort to boost his chances of becoming the RNC chair.
Split into simpler sentences: In 2008 Michael Steele left the RLC, of which he was a founding member, citing disagreements over endorsing primary candidates. Some contend that his departure was an effort to boost his chances of becoming the RNC chair.