A retracted endorsement by a former member of Congress has produced an early spark of disagreement between two Democratic candidates in Illinois’ highly competitive 10th District north of Chicago.

Dan Seals, the losing Democratic nominee in 2006 and 2008, sent out a fundraising e-mail touting the backing of ex-Rep. Abner Mikva, the district’s congressman from 1975 to 1979 and who later served as a federal appellate judge and as Bill Clinton’s White House counsel.

But Mikva has decided to sit out the 2010 Democratic primary, in which Seals’ most threatening opponent is state Rep. Julie Hamos.