Former Massachusetts governor Mitt Romney and Rep. Jesse Jackson Jr. are likely to emerge as the key winners of Tuesday’s primary contests in Illinois.

In a GOP nomination contest that has stretched on much longer than expected, polls show Romney as the favorite over ex-Pennsylvania senator Rick Santorum in President Obama’s backyard. The state fits the profile of places where Romney has done well throughout the year: fewer than half of the voters are likely to be evangelical Christians, a higher percentage of the electorate will be college-educated than in last week’s contests in Alabama and Mississippi, that Romney lost, and the state includes a large metropolitan area (around Chicago) where the ex-governor is likely to dominate among more moderate Republicans.

If he wins, Romney would further expand a delegate lead that seems increasingly insurmountable for his rivals. Romney has 443 delegates, according to NBC News, still less than half of the 1,144 needed for the nomination, but more than the combined totals of his opponents. (Santorum has 184, former House Speaker Newt Gingrich 137, and Rep. Ron Paul (R-Tex.) 34).

But Romney’s winning streak is likely to be short. Republicans in Louisiana will vote on Saturday, and a much more evangelical and conservative electorate there favors both Gingrich and Santorum.

Just as surprising as a Republican primary stretching deep into March, is the challenge Jackson, Jr faces. The son of the famous civil rights activist won his seat in the South Side of Chicago in a special election in 1995 and has cruised to reelection in the years since.

But his Chicago-based district has been changed, under redistricting, to one that is 54 percent black, compared to around 68 percent before. And former congresswoman Debbie Halvorson, who represented a district outside of Chicago from 2006 to 2010 before losing reelection, is running a strong challenge against Jackson.

Jackson has seen his popularity in the district dip amid controversies over an extra-marital affair he had, as well as unsubstantiated allegations that he played some improper role in the saga over who then-Gov. Rod Blagojevich would appoint to replace Obama in the Senate after the 2008 elections.

Aware of his predicament, he has campaigned more aggressively than ever to keep his seat, and polls show him very likely to win.

Follow Perry Bacon Jr. on Twitter at @perrybaconjr