Pennsylvania happens to be the physical location of the latest contest between Senators Clinton and Obama for the Democratic nomination. But in terms of political culture their duel is situated in Mrs. Clinton’s original home and Mr. Obama’s current one — Chicago. You can even say that the battle is between two neighborhoods on the South Side of the Windy City.

The first of those is Bridgeport, the down-to-earth district from which Richard Daley, the father of the current mayor, ruled the city in the 1950s, 1960s, and 1970s. Daley was famous for his efficiency — he got the snow plows out in the blizzard of 1967. As mayor, he reigned so successfully that he gave new meaning to the words “boss,” and “clout.” At its best, Bridgeport is reliable. At its worst, Bridgeport is numbingly corrupt.

The other neighborhood is Hyde Park, the base for Democratic reformers seeking to supplant the party establishment. I grew up in this college community and I love it. The discourse there tends to the polysyllabic.

Mrs. Clinton would be appalled to be paired with “the boss,” Daley. Though she grew up in Park Ridge, her early political life included making rounds among the South Side Left. That was her Saul Alinsky period, when she worked with Obama-type people who dropped phrases like “the harmony of dissonance.” The Illinois people she and Bill worked with while he was governor hated the “Machine” — Daley’s establishment. Even today, the Clintons favor gatherings of big brains — when Bill was president, they liked to attend Renaissance Weekend, loosely modeled after Davos. But long before there was Davos, there was Hyde Park.

But the Clinton campaign thus far has been an exercise in Daleyesque clout. She rewarded New Yorkers from her post as their senator, and correctly predicted that the Empire State would pay her back with electoral votes.

She worked for unions, which is why James Hoffa’s endorsement of Mr. Obama came as a shocker and why Gerald McEntee of the American Federation of State, County and Municipal Employees was in Pennsylvania stumping over the weekend. She is the womens’ candidate. Clinton’s “3 a.m.commercial,” the one in which she suggests she is the one who can get the job done, is the foreign-policy equivalent of Daley’s promises that his snow plows would be ready come the next STORM. Mr. Obama by contrast is pure Hyde Park, as scintillating and idealistic as a professor. At its best, Hyde Park represents liberalism at its best — a place where free-market liberals can send their children to school with progressive liberals.

At his best, Mr. Obama also represents that liberalism — a thoughtful and colorblind view of the world. At his worst, Mr. Obama is the classic Hyde Park snob. That is to say he pretends to be tolerant even as he proves himself intolerant. This is what came out in Mr. Obama’s description of small-town voters as gun slingers who nurse “antipathy to people who aren’t like them.”

So what does Bridgeport versus Hyde Park tell us about Pennsylvania and beyond? The Bridgeport in Hillary is what gave her the lead over Mr. Obama. A poll released by the Pittsburgh-Post Gazette and MSNBC just before the vote found more Clinton supporters than expected among gun owners, bowlers, and beer drinkers — in short, a Bridgeport-type crowd. These voters don’t care if Mrs. Clinton contradicts herself, as long as she delivers.

But the Bridgeport-Hyde Park split also bodes well for Mr. Obama. Contrary to the spin, Hyde Park-style figures sometimes triumph on the national stage, especially in periods like now, when Washington is looking destructive, wasteful, or inept.

Paul Douglas of Illinois, a sort of pre-Bama, got to the Senate on sheer good character. So did Abner Mikva, a congressman who later became a federal judge and the Clintons’ counsel. Gene McCarthy and George McGovern didn’t make it to the presidency, but Jimmy Carter did. Mr. Carter was not even a Northerner, but he did feature that “I live in my own head” idealism familiar to those who live and work along the Midway.

The trouble with Hyde Parkers isn’t how they campaign, but how they govern. Once they get in office, they find themselves building their own machines. Since they are new to the game they tend to play it worse than the old pols.

From Mrs. Clinton’s point of view the rest of the Democratic contest is all about forcing Mr. Obama to reveal his interest-group apparatus now rather than later, so she can attack it. New York is a long way from Chicago, but the dispatch with which that old party man Sheldon Silver, the speaker of the New York State Assembly, dethroned Governor Spitzer, the self-proclaimed king of change, was an example of what a Bridgeport can do to a Hyde Park.

If a Hyde Parker in office survives, he eventually morphs into a Bridgeporter. That is what may happen to Mr. Obama. In other words, the Republican opponent, Senator McCain, may be going crazy campaigning against two different figures. But in reality he’s running against a single opponent — the evolving Democratic politician from the ultimate political city, Chicago.

Miss Shlaes, a senior fellow at the Council on Foreign Relations in economic history, is a columnist for Bloomberg News.