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As March began, the ten contests on Super Tuesday--March 6th--loomed large. It was commonly understood that the Republican presidential primary had become a regional battle. The main battleground was Ohio, a Midwestern state where Rick Santorum had been polling very well prior to the Michigan primary at the end of February. Mitt Romney's campaign put all available resources into Ohio and began to close the gap.
Nationally, public opinion began to turn, slowly, against Santorum. Santorum's strength during the previous month was surface-deep; it was based on voters' lack of familiarity with his weaknesses. Still, Ohio was in his backyard. With Romney pulling ahead in the final polls, Newt Gingrich supporters in Ohio made a last-second shift over to Santorum. But it was not quite enough: Romney won Ohio by one point.
The remaining Super Tuesday states were split, with Romney winning most of them, but with Santorum doing well in the South. Critically, Santorum and Gingrich had failed to get on the ballot in Virginia, adding another win to Romney's column. And Gingrich won in his home state of Georgia, cutting into delegates Santorum would have otherwise easily taken.
Romney's win in Ohio made it readily apparent that he was the man to beat. Santorum's losses in Ohio and Michigan blunted all of the momentum he had gained during February. Yet, the split-decision on Super Tuesday brought something important to light: After a certain point, presidential primaries are based on delegate math, not momentum. In March, Romney's campaign went into full delegate mode, gathering up delegates from every little contest they could. This included several contests in island territories like Guam, Puerto Rico, and the U.S. Virgin Islands. Romney was able to accumulate a disproportionate number of delegates from these contests.
On March 13th, the three leading candidates converged on the Deep South for the primaries in Alabama and Mississippi. Because of Gingrich's strength in that portion of the South, the Anti-Romney vote was split. Early polls suggested Romney might even be able to exploit the split to win in one or both of the states. But as before, Gingrich voters strategically shifted, giving both states to Santorum. Now, finally, Gingrich's campaign was truly dead--though he refused to drop out.
Unfortunately for Santorum, it was too late. The delegate math increasingly favored Romney, who was able to win on his own turf by wide margins, while Santorum's wins usually involved prevailing by smaller margins against Romney or Romney/Gingrich. The possibility of Santorum actually winning a majority of the delegates was slim; instead, it seemed as though he was merely attempting to force a contested convention. That, along with an increasing public awareness of Santorum's faults, caused Santorum's support to erode.
On March 20th, the new dynamic was plain for all to see. Romney won the Illinois primary by a whopping 12 points. Gingrich voters had shifted to Santorum again--basically taking Gingrich out of the equation--but it didn't do much good. Santorum's last, best hope had been that Gingrich's collapse would allow the Anti-Romney vote to coalesce. The Anti-Romney vote did unite behind Santorum, but there weren't enough Anti-Romney voters left. Even in Wisconsin, another Midwestern state, early polls looked good for Romney.
As March came to a close, the Romney-favoring April calendar approached. Romney was in a dominating position. It did not appear likely that the other candidates could stop Romney from getting a majority of the delegates and winning the nomination.