Why is Chicago important?
Chicago - where former presidential chief of staff Rahm Emanuel is running for mayor - has a reputation as a key city in the national politics of the US. Why?
Chicago was once home to arguably the most powerful local politician in America.
Richard J Daley was mayor of the city for more than 20 years, the man at the apex of a political system known as the Machine.
Chicago was not the only place in the US to be dominated by Machine-style politics, but it lasted longer and grew bigger there than in most American cities.
Machine politics was a system of extended quid pro quo, accompanied by a rigid political organisation from grass roots upwards.
It was done by "by using patronage, by providing favours, by co-opting possible enemies", says Dominic Pacyga, author of Chicago: A Biography.
At the bottom of the system were ordinary voters. At the top was the mayor. In the middle was a hierarchy of captains and lieutenants who controlled each ward.
Their aim was to get out the vote, and co-operative voters were rewarded.
"Early on it was jobs for people who would be employed by the machine. It is all designed to get out the vote," says Elizabeth Taylor, a journalist on the Chicago Tribune and co-author of American Pharaoh.
The Machine - and Richard J Daley - had its finest hour in 1960 with the election of John F Kennedy. An extraordinary voter turnout in Chicago was enough to win the state for JFK in a closely fought election with Richard Nixon.
"As JFK said: 'It's the ball game'," notes Taylor.
The circumstances were such that Republic activists and journalists repeatedly investigated allegations of voter fraud.
But Daley and his Machine were cockahoop. Chicago had decided the presidential election.
Since then, despite the decline of the Machine, Chicago has remained a key place for Democrat strategists.
"Chicago has been an important barometer of Democratic politics for a long time," says Pacyga. "It is vital for a national presidential election to take Chicago and take Illinois."
Daley's son, Richard M Daley has also managed more than 20 years at the helm of Chicago, despite the decline of the Machine.
And Chicago retains a significance in national politics because of the nature of its Democrat base. It is a city which has managed to prosper despite the decline of manufacturing industry, which has ethnic political powerbases and which is not on the fringes of the Democratic party.
"[They are] very centrist Democrats The Daleys have almost been Republicans in some ways - not radical or even progressive," says Pacyga
The state of Illinois has often had Republican governors, although in the last five presidential elections it has voted Democrat.
Now it has provided a president.
"Obama is extremely popular still in Chicago," says Pacyga. "He is the first Chicagoan to be president. He identifies with the city quite strongly."
And there is a geographical significance with Chicago at the centre of the country, says Taylor.
"It matters as a capital between the coasts. It has been the centre of America."
The city has been pivotal in the three great migrations in the US - the wave of immigrants from Europe, the movement of black families from the South, and the shift from rural to urban areas.
"Built on that, it became the quintessential American city," says Taylor.