(CNN) -- Rick Santorum said a few days ago an Illinois win could guarantee him a path to the nomination. Now a double-digit victory in President Barack Obama's home state may do the same for Mitt Romney.
First, the good news for Santorum: He held on to his edge with working-class and rural voters, winning both categories Tuesday in Illinois. He continued to claim Republicans looking for strong character and conservative bona fides in their presidential candidate. And he was the top pick among the most religious voters: regular churchgoers, evangelicals and those who think the religious beliefs of their party's nominee are important.
Now, the bad news: According to exit polls, Romney won virtually everyone else.
Romney's victory was fueled by massive majorities of voters with college degrees and six-figure incomes. But by narrower margins, he claimed nearly all other demographic blocs, too, including groups he's struggled to win throughout the primary season, such as the strongest tea party supporters.
Male voters backed Romney over Santorum by a double-digit margin. And Illinois voters didn't just dub him the most electable candidate in the race, a title he usually claims; they also named him the White House hopeful who best understands the problems of average Americans.
A Gallup survey released Tuesday, as Illinois votes rolled in, suggested Santorum remains the top pick for Midwestern primary voters. That preference just isn't showing up at the ballot box: Tuesday's Romney victory was his third Rust Belt win in as many contests.
So does Tuesday's result mean voters are finally ready to put an end to the fractious primary fight? Not necessarily: Roughly two-thirds of Republican primary voters in Illinois said they'd rather see the candidate they back finish first than see the race end fast. A Newt Gingrich-less race -- a two-man battle between Romney and Santorum -- wouldn't have handed the former senator from Pennsylvania the state. But it would have cut the Romney margin of victory by more than half.
Still, a looser, more comfortable Romney was the only candidate left in the state Tuesday night, delivering a biting election night speech focused solely on Obama. He may have spent multiples more on attack ads over the past few weeks than the rest of the field put together; but on the stage Tuesday night, his GOP rivals rated a single, positive reference, almost in passing.
And the Romney team is also laying out an even simpler message than Santorum's: At this point, it says, the former Massachusetts governor is the only candidate with a realistic chance of claiming the top spot on the ticket.
The Santorum team pointed to his strong showing in the most Republican, most conservative parts of the state, and the delegates he'll gain in those areas. But fewer than one in eight of Tuesday's votes were cast in the mostly rural downstate. Nearly three in five of them came from the Chicago area, where Romney scored a 20-point advantage.
Santorum did come within striking distance of Romney -- a relatively strong showing that stands in stark contrast to a fading Newt Gingrich, locked in a battle with Ron Paul for a third-place finish in the single digits. But he still ends the night with a far bigger deficit than he began it, with Romney claiming the lion's share of the 54 delegates at stake.