After losing the South to Rick Santorum a week ago, Mitt Romney did what he had to do in the Republican presidential primary in Illinois on Tuesday and perhaps a little more. His victory was far more impressive than it was in Michigan or Ohio. He added to his delegate lead and improved his support among key parts of the GOP coalition.

But another way to look at Tuesday’s results is that Romney did only what he was expected to do. He won in a big Northern state with an electorate tailor-made for his brand of moderate conservatism. In that sense, the outcome in Illinois did not change the Republican race so much as it confirmed the patterns that have taken hold in the past six weeks.

Over the next two weeks, two states will offer the opportunity for the leading candidates to break the mold that has existed since Santorum won three contests on a single night in February and staked his claim as Romney’s principal rival. The first is Louisiana, which will hold its primary on Saturday. The second is Wisconsin, which, along with Maryland and the District of Columbia, will vote on April 3.

Tuesday’s results showed that the nomination contest has turned from the high drama of winter to almost tedious predictability in the spring. Romney will win more states than he loses while continuing to rack up more delegates than his rivals. But Santorum still may have the capacity to win states with a high percentage of evangelical Christians, very conservative Republicans, strong supporters of the tea party movement or voters with family incomes below $100,000.

Romney’s sizable win in Illinois will generate talk among his loyalists that it is time to close ranks and bring the race to a close. In reality, it may take a breakout in an unexpected place to accelerate or, far more improbably, put a real brake on what otherwise appears to be Romney’s long, slow march to victory.

Santorum will be favored Saturday in Louisiana, a Southern state with a conservative electorate that should be to his liking. A Romney upset would deal a significant setback to Santorum’s hopes of carrying on this battle to the end of the primaries in June. Romney wanted that breakthrough victory in Mississippi last week but ended up third. He’s unlikely to raise expectations in Louisiana.

Santorum’s real hope to shake up the race and raise new doubts about Romney as the leader of a conservative party will be in Wisconsin. The Badger State will present an interesting challenge. It is a kind of geographic boundary between the states in the industrial heartland that Romney has won — Illinois, Michigan and Ohio — and the Midwestern states west of the Mississippi River — Iowa, Minnesota and Missouri — where Santorum has found support.

Wisconsin is both industrial and agrarian. It could be a competitive battleground in November. It has been a political hotbed for the past year. Its GOP leadership includes two conservatives — Gov. Scott Walker and House Budget Committee Chairman Paul Ryan — who are prominent role models for the new Republican Party.

A Santorum victory in Wisconsin would be unsettling to a Republican establishment eager to bring the nomination battle to a close. But can Santorum replicate his previous Midwest success and change perceptions of the race? The odds say no, which is why a surprise in Wisconsin would be so significant.

For Romney, Wisconsin presents an opportunity to put an exclamation point on his other Midwestern primary victories. The electorate is likely to favor the former Massachusetts governor. The state doesn’t have enough evangelicals to give Santorum the kind of built-in help he needs. His hope may lie in finding enough blue-collar conservatives who respond to his message.

Set against the other states that have voted this year, the exit polls from Illinois confirm the solidity of the race. The surveys help to explain why Santorum never really had a chance to upset Romney there, even if he had been able to come marginally closer to parity in the amount of money he and his super PAC could spend on television ads, robocalls and other efforts to reach voters.

Romney has won every state that has had an exit poll and in which white, evangelical Christians accounted for less than 50 percent of the electorate. He has lost every state where evangelicals made up more than 50 percent of the electorate. Santorum has won five of those, and Newt Gingrich took two.

In Illinois, about four in 10 voters said they were evangelicals, on a par with Michigan, lower than Ohio and lower by far than in the Southern states and Iowa. Santorum did slightly worse among evangelicals in Illinois than in Michigan and was on a par with his showing in Ohio. But Romney’s percentage was higher than in those other two states — an encouraging sign for his campaign.

A similar rough boundary line exists for the electorates based on ideological leanings. Romney has won every state with exit polls in which “very conservative” voters have accounted for fewer than 35 percent of the vote. He has lost the states in which the percentage is greater than 35 percent.

In Illinois, the percentage of very conservative voters was a little less than one in three — about the same as in Michigan and Ohio. Romney’s support among these voters fell roughly in between his showings in the other two heartland states.

Patterns based on income and tea party supporters are less sharply etched but also relatively clear. In general, the more voters there are with family incomes above $100,000, the better Romney does. The higher the percentage of strong tea party supporters in a state, the better his opponents perform. The Illinois electorate fell on the upper end of states with a relatively high percentage of high earners and was around the middle in the percentage of strong tea party supporters.

About one in three voters Tuesday said that defeating President Obama was the biggest factor in their decision, and Romney won more than two in three of them. But two in three said they don’t favor bringing the race to a speedy conclusion.

Tuesday was a very good night for Romney, in sharp contrast with last week. He started ahead and stayed well ahead. But he has had other big nights this year, only to be followed by setbacks, disappointments and doubts, which is why his campaign seems resigned to a long race.

Perhaps Romney’s showing will trigger the kind of winning streak that would significantly speed up his ability to achieve the 1,144 delegates needed to clinch the nomination or generate pressure on the others to leave the race. Perhaps Santorum can find a way to expand his support. Absent that, the contest will grind on until summer — toward its predictable conclusion.

Polling director Jon Cohen contributed to this report. For previous columns by Dan Balz, go to