WASHINGTON (CNN) -- Former Sen. Zell Miller, a Georgia Democrat who supported President Bush in 2004, will head a new group of Democrats supporting Pennsylvania GOP Sen. Rick Santorum's reelection bid. "I am not involved in any other race in the country," Miller said during a radio interview Monday, according to a news release from Santorum's campaign. "I am only doing this for Rick Santorum. I believe in Rick Santorum's leadership that much."