(CNN) -- Turns out the U.S. territories are very, very good to Mitt Romney. He romped in the commonwealth of Puerto Rico on Sunday, so much so that he took all 20 delegates. Oh, how Romney would love a romp in Illinois on Tuesday.
It wouldn't put him over the top, but it would put Romney solidly back on terra firma with at least a breeze at his back, maybe even enough of it to push him through what is likely to be another tough Southern primary, this one on Saturday in Louisiana, decidedly not Romney country.
An Illinois romp seems unlikely. For starters, exit polls from the Republican presidential primary there in 2008 found 42% of voters self-identified as born again or evangelical Christians, the fuel that lights Santorum's fire. The natural habitat for Santorum voters is downstate Illinois.
Romney types are in the north around Chicago and its suburbs, where typically three-quarters of Republicans vote. Advantage Romney, except evangelical and Christian conservative voters have been turning out in big numbers for Santorum.
That's not quite the case with Romney's following, which has been less enthused much of the primary season. He will have to do a better job in Illinois than he did in Arkansas or Mississippi at getting his people to the polls.
Because of the competing demographics and that emerging enthusiasm gap, a big Romney win in Illinois doesn't seem in the cards, but some kind of win is darn close to mandatory.
Say all you want about his lead in the delegate count, Romney can't afford another gloomy Tuesday in the kind of state in which he has done best (think Ohio and Michigan).
No matter what, Romney will win delegates in Illinois and end the night with more total delegates for the primary season than anyone else.
Somehow, though, Illinois doesn't feel like one of those places he can toss off with the mathematics of the delegate count. Illinois feels like a must-win for Romney.
This weekend in Effingham, Illinois, Santorum was feeling the possibilities.
"This is a pledge," he said. "If we're able to come out of Illinois with a huge or surprise win, I guarantee you, I guarantee that we will win this nomination."
Mathematically, it's unlikely Santorum could win the nomination outright during the primary season, but he might prevent Romney from winning it, too.
If Romney loses Illinois, the "can't-seal-the-deal" sign over Mitt Romney goes neon.
It may light up the way to Tampa, Florida, and a brokered convention.