Waukesha is just the kind of suburb where Romney has performed well in other states. He was counting on voters in Waukesha and the other heavily Republican communities on Milwaukee's outskirts to offset Santorum's likely strength in rural and small-town Wisconsin. And so they did.
Looking ahead, Pennsylvania is, for Santorum, the most promising of the states holding the next round of primaries on April 24. Romney is favored in the others — New York, Connecticut, Rhode Island and Delaware.
If he makes it beyond that, May looks better for Santorum. He has expressed high hopes for the primaries in Indiana, North Carolina, West Virginia, Arkansas, Kentucky and Texas.
But the closing round of primaries in June will be in states where Romney could finally have a shot at crossing the threshold of 1,144 delegates needed to win the nomination. Among them: California, New Jersey and Utah.
Times staff writers Mark Z. Barabak and Seema Mehta contributed to this report.