Chicago heavyweights Rod Blagojevich, Barack Obama and Richard M. Daley in 2007.

As Illinois Gov. Rod Blagojevich ponders the question of who should take President-elect Barack Obama’s barely warmed seat in the United States Senate, it’s safe to assume that the concerns of downstate and Metro East residents are not at the top of his list of priorities.

Indeed, of all the names being bandied about as replacements for the state’s junior senator, who planned to resign his seat Sunday, none of them hails from south of the Des Plaines River. This is a Chicago matter, as Democratic politics in Illinois usually are.

Given Mr. Obama’s new prominence, the matter of his replacement offers the rest of the world a glimpse at the fratricidal environment from which he emerged only four years ago. This should be entertaining, as well as reassuring: With due apologies to “New York, New York,” if Mr. Obama could make it there, he can make it anywhere.

The primer begins with Mr. Blagojevich himself, who still spends most nights at home in his bungalow on Sunnyside Avenue in northwest Chicago about 10 minutes from Wrigley Field. He was elected governor in 2002 and reelected in 2006. There’s never been a dull moment.

Mr. Blagojevich’s political patron was his father-in-law, Chicago Alderman Richard Mell, but in 2005, the two men had a very public falling out. By then, Mr. Blagojevich had forged a new alliance with state Senate President Emil Jones of Chicago. Mr. Jones had become a powerhouse in the Senate after losing a primary race in a special election for Congress in 1995 to Jesse Jackson Jr., son of the civil rights leader and himself a potent political force. Mr. Jones also served as a political mentor to Mr. Obama.

Mr. Blagojevich badly needed a legislative ally, inasmuch as he’d antagonized House Speaker Michael Madigan, yet another powerful Chicago Democrat. Indeed, for much of the last four years, the Illinois General Assembly has been gridlocked, in large part because of the Blagojevich-Madigan feud.

Meanwhile, Mr. Madigan’s daughter, Lisa Madigan, was elected Illinois attorney general the same year Mr. Blagojevich became governor and has staked out a position as a tough consumer crusader and a powerful political force in her own right. She often is mentioned as a primary opponent for Mr. Blagojevich, should he seek a third term in 2010.

So now comes Mr. Blagojevich with the absolute right to appoint a United States senator to serve the final two years of Mr. Obama’s term. Does he appoint:

• Mr. Jackson, 43, whose supporters, including his father, argue that by rights, the Senate’s only African-African member should be replaced by another African-American?
• Mr. Jones, 73, also an African-American, but less likely than Mr. Jackson to run for reelection in 2010?
• Ms. Madigan, 42, thereby removing her from the governor’s race in 2010 and possibly appeasing her father?
• Or someone else: State Treasurer Alexi Giannoulias, 32, another possible gubernatorial challenger in 2010 and a hoops buddy of the president-elect? Tammy Duckworth, 40, a disabled Iraq war vet, an Asian-American and a favorite of the state’s senior U.S. Senator, Dick Durbin? (Mr. Durbin is yet another Illinois Democrat who doesn’t speak with the governor.) U.S. Rep. Jan Schakowsky of Evanston, 64, a favorite of Chicago Gold Coast liberals? Or maybe a wild card?

Mr. Jones is the safest best. If he can be persuaded to step down in two years, it would let everyone else fight it out for his seat. But Mr. Blagojevich very seldom does the safe thing. With his approval ratings now at 13 percent, he can afford to roll the dice — and probably will.