After Mitt Romney’s sweep last night and a fresh delegate haul, the road ahead gets tougher for Rick Santorum.  Santorum never really came close in Arizona, but he had a lead in Michigan until a mediocre debate performance a week ago gave Romney an opening to take his native state by a small but significant margin of 32,000 votes, about three percentage points of the overall vote.  Turnout appears to be slightly higher than in 2008, and that means that Romney can avoid another knock about his impact on voting in the primaries being depressed in his wins.  Even the hope that Santorum might end up with more of Michigan’s delegates, thanks to rules that allocate them by Congressional-district votes, ran aground this morning:

Former Massachusetts Gov. Mitt Romney won the popular vote by a 41-38% margin as well as the tally in seven of 14 congressional districts, most of them in southern Michigan.

Former Pennsylvania Sen. Rick Santorum won six congressional districts, including the 1st district, which includes the Upper Peninsula an a portion of northern Lower Michigan by just two votes. All of Santorum’s wins came in the northern and western portions of the state. …

As a result, Romney wins 21 delegates from the congressional district results, according to results posted by the Michigan Republican Party, but only 14 of those delegates will be allowed to vote at the national convention because the state broke national GOP rules by moving its primary before the Super Tuesday contests next week.

Santorum wins 18 delegates from the congressional districts, but only 12 of those people will be able to vote at the national convention.

The statewide popular vote will be distributed between Romney and Santorum on a proportional basis with 14 at large delegates at stake, but only two of those delegates will have voting privileges. How those will be divvied up hasn’t been determined.

Santorum’s team claimed a moral victory in a close second-place finish:

“A month ago they didn’t know who we are, but they do now,” Santorum told supporters gathered in a downtown hotel. “We came into the backyard of one of my opponents, in a race that everyone said, ‘Well, just ignore, you have really no chance here.’ And the people of Michigan looked into the hearts of the candidates, and all I have to say is: I love you back.”

Santorum’s advisers noted that Santorum and Romney essentially split the delegates in the Michigan contest because of new party rules, regardless of what the popular vote may have been. Senior strategist John Brabender and others suggested Romney would emerge from Michigan as a weaker candidate.

“God bless him for spending a fabulous amount of money to come into his home state to eke out a victory in the total count and to walk away with many fewer delegates than anybody thought humanly possible two weeks ago,” Brabender said.

The problem with that spin is that, eventually, wins matter, and not just in delegate counts.  One does not win the nomination through a series of second-place finishes.  For a campaign that runs one campaign at a time rather than an organization competing in multiple states at a time, victories are even more important.

In six days, the candidates will compete again in ten states for the Super Tuesday threshold, and the consensus is that Ohio will hog the spotlight.  Georgia might come into play, too, if Newt Gingrich can’t hold onto his lead in his own native state, and Santorum has a big lead in Oklahoma that Romney will not likely bother to challenge.  Santorum didn’t get on the ballot in Virginia, and has a smaller slate of electors in Tennessee thanks to a failure to qualify them.  Ohio has the largest delegate haul next week, and it also consists of the kind of blue-collar, Rust Belt voters that Republicans need to draw to win in November.

So far, Santorum has a lead in the RCP poll average of about eight points, but that may change with the loss in Michigan among the same kind of voters.  Santorum cannot afford another loss in the Rust Belt, especially since Romney is likely to do well in most of the other Super Tuesday contests.  Since all of the binding contests on Super Tuesday are proportional-allocation primaries, Santorum will get a significant number of delegates from second-place finishes again, but without a couple of big wins, Romney will keep adding to his delegate lead and making the case for donors to get on the bandwagon now.

It’s not over for Santorum, but a win in Ohio is a must.  Expect to see Romney and Santorum in Buckeye country all week long.

Update: I had forgotten about this, but my friend Salena Zito of the Pittsburgh Tribune-Review reminds me that Santorum won’t be on the ballot at all in three of Ohio’s Congressional districts:

Political strategists consider Ohio a critical win for the eventual Republican nominee because none has won the White House without winning the state.

Among 10 states holding Super Tuesday primaries on March 6, Ohio will award 66 delegates to the Republican National Convention. Santorum is not on the ballot in three of the 16 congressional districts, potentially putting him at a nine-delegate disadvantage.

That complicates matters for winning the state, obviously.  If Santorum loses Ohio overall because he couldn’t make the ballot in three CDs, that won’t be an excuse — it will become a reason for voters in later contests to stick with the candidate with better organization.  Santorum will need to win by enough in the other thirteen CDs to overcome his omission, and that will be a very tall order.

Update II: Actually, voters in those districts can vote for Santorum — but he can’t win the delegates, according to Politico:

All six major GOP candidates have been certified and will appear on the Ohio ballot, according to a list released by the Ohio secretary of state’s office today. But Rick Santorum, the release said, did not file delegates in the 6th, 9th or 13th congressional districts — and loses his chance at getting any delegates in those districts.

Forty-eight of the state’s 66 delegates are awarded proportionally based on the vote in each congressional district — three per district — and the remaining 18 delegates are awarded based on the at-large vote statewide. That means that while Santorum can get votes toward the at-large total in those three districts, he has no shot at taking a share of the nine total delegates those districts will award.

That’s still going to be an issue in the Ohio election, but it’s not as bad as it first looked.  Thanks to Daren B for the update.