From the Civil War through the early 20th century, Illinois consistently voted a few points more Republican than the rest of the country. This changed with the Democrats' nomination of Al Smith in 1928, which drew white ethnics to the voting booth in droves. They kept voting, and from 1928 through 1976 the state was consistently at the center of American politics. Democrats drew their strength from Chicago, while Republicans dominated downstate and the suburban collar counties.
That changed during the 1990s, when Bill Clinton's appeal to suburban soccer moms moved the northern suburbs toward the Democrats. Illinois became a solidly Democratic state, to the point where a Senator facing serious ethics allegations like Carol Moseley Braun only lost by a few points to Peter Fitzgerald in 1998. Fitzgerald opted not to run for a second term in 2004, and an obscure state Senator named Barack Obama took the seat in a landslide over conservative Republican Alan Keyes. When Obama was elected President, Governor Rod Blagojevich appointed Roland Burris to the seat; Burris also opted not to run.
This set up a top-notch fight between Republican Mark Kirk and Democrat Alexi Giannoulias. Kirk's resume was especially interesting; he had represented the north Chicago suburbs for a decade in Congress, and thus had shown strength in a swing area of the state.
But neither candidate has acquitted themselves particularly well. Giannoulias received a round of negative publicity from the collapse of his family bank, while Kirk was caught exaggerating his military record. Kirk ended the second quarter with four times Giannoulias' cash-on-hand, and leads in most polls. RCP sees this as the purest of tossups.
Sean Trende is Senior Elections Analyst for RealClearPolitics. He can be reached at strende@realclearpolitics.com.