The Mississippi and Alabama contests — like so many other Tuesday primaries before them — were supposed to decide the fate of the GOP presidential nomination.

Except Rick Santorum's double wins only tabled the decision for a future date. In this case, that might be March 20, when voters in Illinois will cast ballots.

So what do we know about Illinois? There are 69 delegates at stake — 15 of whom are unbound and 54 of whom are bound.

Polling is scant. Last week, the Chicago Tribune released a survey showing Mitt Romney winning 35 percent of the vote; Santorum was second with 31 percent; and Newt Gingrich took 12. Unfortunately, that’s the only meaningful poll of the state in the past five months.

The Tribune’s survey suggests an enormously fluid race, with 46 percent of likely voters saying they could change their minds before next Tuesday’s contest.

That’s a boon for Romney, who’s already begun advertising in the state and can flood the airwaves in the days leading up to the primary. But he’ll be doing it against a new surge of momentum for Santorum after Tuesday night’s wins, and at a minimum, Romney’s financial advantage and Santorum’s momentum should cancel each other out.

After all, Romney outspent Santorum in the South, only to lose to the former senator.

The usual demographic breakdown seems to apply in Illinois as well. Santorum runs better among the “very conservative” (+14 percent), while Romney leads among centrists by 22 percent. Santorum also wins evangelicals, while Romney wins women and suburban voters.

In short, you can expect an election very much like Michigan's and Ohio’s — both of which Romney won. The former Massachusetts governor will likely try to run up the score in wealthier Republican suburbs, and Santorum will likely work to turn out conservative rural voters.

But there are two big wild-cards that could threaten to upend some of the more predictable dynamics.

First, Illinois’ primary system is open. In other words, any registered voter can show up and vote. In Michigan, prominent Democrats, including the liberal site Daily Kos, encouraged Democrats to vote for Santorum to embarrass Romney and extend the primary season. Romney eventually won, but Democrats did, in fact, make the race more competitive. Santorum won Democrats by 33 percent, and that made up 9 percent of the entire voting electorate.

In Ohio, Santorum once again routed Romney with Democrats, but Democrats only made up 5 percent of the electorate — barely one-half of Michigan’s. In other words, “Operation Hilarity” — as Dems dubbed it — faded. If Democrats had shown up in Ohio at Michigan-like rates, Santorum would have won Ohio and shifted the entire race.

A big question is how many Democrats will show up in Illinois. In Michigan, there were two weeks of dedicated coverage before the primary vote, which gave Democrats plenty of time to organize and develop a mischief-making campaign. But Illinois’s primary is just a week away and, thus, a “Hilarity” movement might not blossom in time to help Santorum.

The second complicating factor is Newt Gingrich’s status in the race. Tuesday’s results furthered his position as a spoiler who can peel enough votes from Santorum to threaten the former Pennsylvania senator’s hopes, but not enough to win for himself. To be sure, Gingrich ran a strong second in Alabama and Mississippi, but the states were must-win for him, and thus far he's performed miserably in the Midwest where Illinois lies.

Gingrich picked up 15 percent of the vote in Ohio (where he campaigned) and 7 percent in Michigan (where he didn’t).

If he stays in the race, as he promised Tuesday night, Gingrich will continue to undercut Santorum, particularly with conservative voters. He could also delay Romney from reaching the 1,144 delegates needed to cinch the nomination.

For example, according to a CNN exit poll, in Illinois’s 2008 primary, 27 percent of voters called themselves “very conservative.” Santorum has been destroying both Romney and Gingrich with that group in the Midwest, but Gingrich still garnered 15 percent of the “very conservative” in Ohio. A similar showing with that bloc in Illinois would soften Santorum’s numbers with the voters he needs to win.

Yet it seems as though Santorum has no choice but to endure Gingrich’s presence, as his spokesman Hogan Gidley told CNN Tuesday night. Gingrich “has every right” to continue running, Gidley claimed, but “if he weren’t in the race at this point, not only would we be beating Mitt Romney in these other states, we’d be beating him badly.”

There’s a chance, though, that with each new Santorum win and Gingrich loss, the race will morph into the one-on-one Santorum wants — himself and Romney. Indeed, the question is whether Gingrich loses supporters who now see the race as distinctly a Santorum vs. Romney affair.

That provokes an interesting question for Santorum. Should he train his fire on Gingrich to try to peel off the former's Speaker's voters, or focus on Romney and try to keep down the former Massachusetts governor's margins in the suburbs?

Another dilemma for Santorum: In Michigan, he took major heat from Republicans for actively courting Democrats through robocalls. To an extent, you could say it might have worked by helping boost the Democratic share of the vote to nearly 10 percent. But it also provoked considerable backlash among the GOP grass roots. Should Santorum woo working-class Democrats and mischief-minded foes of Romney, and if he does, how should he do it?

All these questions will have to be answered very quickly. Illinois — and its enormous potential for Santorum — is only a week away.