A sex scandal before an election might be expected to help the opposing party's candidate, but Republican Rep. Mark Souder's resignation in Indiana's 3rd congressional district could in fact dash Democratic hopes for a possible pick up this fall. Souder, who was seeking a ninth term, disclosed Tuesday that he had an extramarital affair with a part-time staffer, and announced he would leave Congress by week's end. An evangelical Christian, Souder was elected in the Republican wave of 1994 after a career as a Hill staffer in both chambers for Dan Coats (R.-Indiana). "I sinned against God, my wife, and my family by having a mutual relationship with a part-time member of my staff," said Souder, 59, in a statement in which he took full responsibility for his actions."In the poisonous environment of Washington D.C., any personal failing is seized upon, often twisted, for political gain. I am resigning rather than to put my family through that painful, drawn-out process."