RANGEBURG, S.C. -- In the midst of the Sen. John McCain's presidential announcement tour comes news that Marlene Elwell -- one of the Arizona Senator's leading social conservative advocates -- has parted ways with the campaign.

Elwell, who was one of McCain's chief liaisons to the faith community, confirmed her departure in a brief telephone interview this evening. She did not offer any further explanation on the decision.

Elwell, who is based in Michigan, rose to prominence in social conservatives as a leading member of Pat Robertson's campaign. She was also a prime mover in the Michigan effort to define marriage between a man and a woman that passed in 2004.

The departure of Elwell comes just days after McCain replaced his longtime finance director Carla Eudy in what communications director Brian Jones described as part of an overall overhauling of the presidential campaign.