Romney can roll up a solid win in Tuesday's presidential primary with a strong showing along the state's east-west Interstate 94, which bisects Milwaukee's GOP-rich western suburbs.
Santorum's fading hopes rest on swamping Romney in cities and towns along north-south Interstate 43, which lead from Milwaukee north through the industrial and blue-collar base of the Fox River Valley.
Wisconsin elections officials are projecting 35 percent of Wisconsin's 3.27 million voters will participate in Tuesday's primary. A large majority of the vote will come from Wisconsin's metropolitan southeast corner and industrial Fox Valley north to Green Bay.
"While you might achieve a victory margin in other places around the state, the percent contribution to the total vote goal, there's just not a lot of numbers there," said Brandon Scholz, a consultant and former executive director of the state Republican Party.
The dynamic favors Romney, whose appeal in the suburbs in Michigan, Ohio and Illinois helped him win those Midwestern primaries this year. Meanwhile, Santorum, who had campaigned aggressively last week in less populous northern and western Wisconsin, planned to return to his home state, Pennsylvania, Monday, all but conceding the state where Romney leads in polls.
Stretches of both I-94 and I-43 also promise to be key general election battlegrounds. The four congressional districts that cover them are represented by Republicans in Congress. Democrat Barack Obama carried the districts narrowly in winning the state easily in 2008, while George W. Bush carried them more easily in his narrow loss of the state in his 2004 re-election bid.
More than Romney, Santorum has ventured away from the suburbs nearest Milwaukee. He was heavily working the upper stretch of the I-43 corridor Sunday, with stops in seven cities including Green Bay, Appleton and Oshkosh.
The former Pennsylvania senator who represented the Pittsburgh area in the U.S. House before that was working hard to come off as a common man. He tossed a few frames at local bowling alleys, swilled beer and stopped in at a Friday night fish fry, a tradition in restaurants and taverns all over the state.
And he's talked a lot about his "Made in America" ideas for reviving the nation's manufacturing sector, which would seem to resonate in a state that's home to motorcycle maker Harley-Davidson's headquarters, plumbing fixture company Kohler and Mercury Marine outboard motors, and dozens of other high-skill, precision manufacturers.
The Fox Valley also is home to the highest concentration of the world's paper manufacturing, good for 10 percent of the employment in and around 16 cities along the river, including Appleton. This blue-collar influence mixes with a conservative evangelical element evident in the anti-abortion billboards that mark the I-43 corridor.
But interviews with voters in these pockets revealed doubts about whether it's paying off in a nomination race Republicans are increasingly interested in winding down and setting up the battle with Democratic President Barack Obama.
Retired sales executive Tom Siewert of Fond du Lac said he's voting for Romney because he thinks it's time for Republicans to focus on November even if it's not the ideal pick for the party. And despite his effort to portray himself as the outsider against the well-funded establishment Republican Romney, Santorum's Washington past is a liability for some voters.
"Senator Santorum is no saint. Nobody is. You spend five, 10, 15 years of your life in politics and you're going to do some things that are not going to look too good to people," Siewert said.
Mary Draheim of Plymouth — halfway between Green Bay and Milwaukee on I-43 — supports Santorum and is bothered by what she calls the GOP establishment's rush to nominate Romney. She calls him the "godfather" of the health care bill Obama signed in 2010.
Impressed by what she describes as Santorum's moral convictions, Draheim said: "I'd rather have him than Romney."
Romney and a pro-Romney political action committee are heavily outspending Santorum and his allies in television advertising, especially in the Milwaukee market.
Still, Santorum drew Laurie Stevens and five of her nine children to a small rally outside his state campaign headquarters in the near-west Milwaukee suburb of Brookfield Saturday.
Stevens is among the heavy pocket of evangelicals in the Milwaukee area Santorum can count on Tuesday. "He stands for what I believe," Stevens said. Of his long odds, she added: "I believe in the power of prayer."
And while I- 94 runs through Waukesha County, home of the state's largest evangelical Christian mega-church, Romney is poised to do better in what has become a heavily suburban county and one of the most GOP-rich tracts in the nation. George W. Bush carried Wisconsin's 5th Congressional District, held for decades by Waukesha County conservative Jim Sensenbrenner, with a whopping 63 percent of the vote in 2004.
Westward residential expansion of the metro area has transformed hundreds of square miles of dairy farms and hayfields into a booming residential area heavily populated by Republicans, including young professionals and retirees.
And Waukesha County has a recent pragmatic hue. In 2008, Republican John McCain collected almost 63 percent in the county, double the more conservative Mike Huckabee's total.
"This primary is about beating Barack Obama," said John Kleczka, a retired accountant and Brookfield Republican who ventured a few blocks east to Milwaukee Friday to see Romney in the iconic Serb Hall Friday night. "It's time to stand by Romney. He can win and do the job."
Longtime Waukesha County GOP activist Edythe Cooper is backing Romney because but she wants the front-runner to end the primary campaign now.
"I don't want any more of this squabbling. I don't want any more of the throat-cutting. If we don't unite, we're not going to win," Cooper said.
Romney has hammered a southern ellipse from Milwaukee west to the suburbs of Democrat-heavy Madison, although he did campaign in the Fox Valley's Appleton Friday.
As he has in other Midwestern states, Romney has spent less time with the grass roots and more time courting GOP establishment figures. True to form, he nabbed the backing Friday of Rep. Paul Ryan.
The congressman is a rising national star. But his district also covers the southeastern corner of the state and catches the southern half of Waukesha County, including the bedroom community Mukwonago.
As traffic whizzed past on I-94 outside a Pewaukee hotel, Ryan introduced Romney to an audience of more than 1,000 conservative activists Saturday, sparking louder cheers than either Romney or Santorum, who addressed the forum later.
Pewaukee Republican Patricia Funk walked away from the forum torn, but leaning toward Romney. "I'm torn, but I'm leaning toward Romney," the retired factory worker said. ""We can fight over values, or we can try to win."