In the Democratic primary, Obama catapulted past the favored candidate, Blair Hull–a securities trader who had spent $29 million on his campaign–after divorce papers alleged that Hull had struck his ex-wife. Last week Obama’s Republican foe, Jack Ryan, quit the race after disclosures that he took TV actress Jeri Ryan, then his wife, to sex clubs in Paris, New York and New Orleans and–according to her claims in a child-custody dispute–pressured her to perform certain acts while strangers watched. After the news broke, GOP leaders in the corn belt told Ryan this would not play well in Peoria. “It seems clear,” says Paul Green, a professor at Roosevelt University in Chicago, “if you’re divorced, don’t run against Barack Obama.”

Illinois Republican leaders are now scrambling to find a candidate to fill Ryan’s spot. Among the possibilities: retired cosmetics executive Ronald Gidwitz; state Sen. Steven Rauschenberger, who ran third in the GOP primary, and Dr. Andrea Barthwell, a black woman from suburban Chicago who works in Washington in the drug czar’s office. Any Republican latecomer will face daunting odds. The Illinois contest offers Democrats a good chance to pick up a Republican seat–and, in the closely divided Senate, that could mean the difference in which party controls the chamber.

The Ryan custody records were opened after a suit by the Chicago Tribune invoking the public’s right to know. Snooping in custody disputes crosses into a thorny frontier in politics. Even some Obama fans see it as dangerously intrusive, including Chicago’s top Democrat, Mayor Richard Daley. “Where does this stop?” he asked. Obama, who is married with two kids, expressed sympathy for Ryan, and watched his stock rise higher still.