MENASHA, WIS. - If Rick Santorum was weighing whether to abandon his quest for the presidency on the eve of the Wisconsin primary that could effectively crush his campaign, he worked hard not to show it.
On Monday, a day packed with rallies, some bowling and a sampling of squeaky cheese curds, Santorum was looking ahead not just to the next round of GOP presidential primaries, but also to a possible floor fight against front-runner Mitt Romney at the party's national convention in August.
"I think it would be a fascinating display of open democracy," Santorum told reporters at a cheese shop in Appleton. "And I think it would be an energizing thing for our party to have a candidate emerge who isn't the blessed candidate of the Republican establishment."
The shorter the fall campaign against President Obama, the better for Republicans, he said. "If I thought that prolonging this race was a detrimental thing for our chances to win in the fall, I may -- I would take a different course.
"But I don't."
Santorum's defiant pose reflected the critical juncture his campaign has reached. The odds are stacked so heavily against him in the battle against Romney that Wisconsin's primary stands as a potentially lethal test of Santorum's capacity to survive.
He has vowed to keep campaigning if he loses Wisconsin. But Romney, the former Massachusetts governor already widely seen as the presumptive nominee, would be viewed that way even more with a Tuesday victory -- and potential wins in Maryland and the District of Columbia as well.
That would dry up potential donations to Santorum and intensify the pressure to drop out.
In a sign of Santorum's fading relevance, Obama's re-election campaign began TV advertising against Romney on Monday.
For Santorum, who clawed his way into contention with months of dawn-to-dusk stumping across Iowa on a budget fit for a college student, there is a big personal dimension to the campaign's next phase -- the prospect of giving up is something akin to heartbreak.
With his improbable rise from the bottom ranks of a crowded field of GOP candidates, Santorum has come to personify the restless faction of Tea Party conservatives who upended the Republican establishment and fueled huge GOP victories across the nation in 2010, notably in Wisconsin. Santorum has also succeeded in uniting conservative evangelical Christians who have long shunned Romney, a feat none of his rivals managed to achieve.
On Monday, Santorum sought to rally conservatives in Wisconsin's Fox Valley with scathing attacks on Romney's mixed record on guns and abortion.
At Sabre Lanes, a bowling alley on Lake Winnebago, the former senator from Pennsylvania reminded more than 100 supporters of his A+ rating from the National Rifle Association and his opposition to the 1990s federal ban on assault weapons.
"I stood tall, and I didn't say that we have a lot of good gun laws in Massachusetts, and I wouldn't touch any of them," Santorum said.
He criticized his rival not only for state funding of abortion during his tenure as governor, but also for a $150 donation that Romney's wife, Ann, made to Planned Parenthood in 1994. Santorum did not mention her by name.
"Governor Romney's actually running ads out there right now suggesting that I'm not pro-life, where Governor Romney and his family have contributed money to Planned Parenthood," he said.
Comparison to Walker
Gesturing toward his wife, Karen, Santorum mentioned that she had home-schooled their seven children.
He also took on the cadence of a Sunday school instructor as he asked, "Why is it that all men were created equal? Because they were endowed by their ..."
"Creator," the crowd shouted in unison, quoting from the Declaration of Independence.
"With certain inalienable rights," Santorum concluded to a burst of cheers.
Paying homage to Wisconsin's besieged Republican governor, Scott Walker, who is facing a recall election in June, Santorum drew a comparison to his own commitment to conservative ideals.
"You elect someone with strong convictions, strong principles, you put them in office, sometimes they surprise you and actually stand by those principles and get things done," he said.
Romney was ignoring Santorum on Monday and taking it to the Democratic president, whom he accused Monday of "crushing dreams" with a "government-centered society."
Obama "takes his political inspiration from the capitals of Europe," Romney told supporters in Green Bay. "His version of a perfect world is a big-spending big government."
The former Massachusetts governor also characterized Obama as out of touch with the woes of average Americans.
"These are tough times for Americans, and he has not done the job people expected him to do," Romney said.
Romney criticized the health- care law Obama championed that is now being reviewed by the U.S. Supreme Court.
"In a government-centered society like this president favors, government bureaucrats can tell you what kind of health insurance you ought to have and ultimately, I'm convinced, they're going to tell you what kind of treatments you can have," he said. "This is where they're going: government directing your health-care life."
Lis Smith, a campaign spokeswoman for Obama, responded with an e-mail attacking Romney's gubernatorial record.
"We've seen what happens when Mitt Romney is in charge and it's greatly at odds with his message today of more jobs, less debt, and smaller government," she said.
The Associated Press and Bloomberg New contributed to this report.