It will prove ironic if the state of Illinois, Barack Obama's home state, will prove to be the state that provided Mitt Romney with the decisive win on his road to the Republican presidential nomination.
It will be hard for any Republican to take Illinois against Obama, but Romney will be grateful to the Illini.
First of all, his margin of victory was ample. Illinois, with a 12% spread, was no squeaker like Michigan or Ohio, where Romney eked out a narrow win against Rick Santorum. Santorum essentially had his one-on-one with Romney, as Newt Gingrich and Ron Paul were non-factors in the Illinois race.
Another important indicator is supplied by the exit polls. They indicate extensive primary fatigue amongst the Republican electorate. This electorate appears to have internalized the press comments that the protracted primary season is playing to the advantage of Barack Obama and hurting the eventual Republican nominee.
That made Romney the beneficiary of strategic voting in this primary. Voters cited his electability and the need to wind up the contest. As Rick Santorum has himself conceded that a contested convention is the optimum scenario he could hope for - and he has no path to a first ballot win at the convention - those who would like a quick knockout turn to Romney.
Romney built his margin in the affluent Chicago suburbs. Suburbia may well prove to be the principal battleground of the 2012 election. In Chicago's Cook County, Romney's margin over Santorum was 57% to 27%.
Rick Santorum could take pride in carrying the rural areas of Illinois. His problem is that he has been there and done that and he needed to show that he could run well in non-conservative areas. The assumption is that rural conservatives will vote Republican in any case.
America, however, for over a century is not a rural country and since the days of William Jennings Bryan, the agrarian vote has been overmatched. The Republicans need to supplement the rural base by cutting in to Obama's advantage in the cities and winning the suburbs - and Santorum has not shown that he can do this.