| ROCKFORD, Michigan
ROCKFORD, Michigan Mitt Romney and Rick Santorum crisscrossed Michigan attacking one another as well as President Barack Obama on Monday in a last-ditch grab for votes a day before a primary that could prove pivotal in choosing the 2012 Republican presidential nominee.
With polls showing the two men essentially tied, Romney and Santorum traded jabs in remarks focused on the U.S. economy, not abortion or other social issues that had begun to dominate the nomination fight.
A Romney victory in Michigan - the state where he was born - would reignite a campaign staggered by Santorum's rise. But a loss would be humiliating and raise significant questions about his candidacy a week before the biggest one-day prize of the primary season, "Super Tuesday" on March 6, when 10 states hold contests.
Romney told voters in Albion, Michigan, that he was gaining momentum. "This sure has been fun these last 10 days or so. We started out about 15 points down in the polls. Now we're leading in the polls," he said.
A Santorum win in Michigan could upend the race and prompt the Republican establishment - concerned that Santorum's strong religious conservatism could make him unelectable - to search for a new candidate to join the race, which picks a challenger for the November 6 election against Democratic President Barack Obama.
A new poll said Santorum had halted a slide in support that began after a weak debate performance in Arizona last week.
The Mitchell Research/Rosetta Stone poll said the former Pennsylvania senator is in a statistical dead heat with Romney, edging him 37 percent to 35 percent after losing the lead last week. The poll's margin of error was 3 percentage points.
"The volatility we thought had changed has not. The race remains very fluid," said Steve Mitchell, president of Mitchell Research & Communications, a Republican firm that polled 858 Republican primary voters.
Romney has a comfortable lead in Arizona, which also votes on Tuesday. A survey by Public Policy Polling conducted on Sunday showed Romney was leading Santorum by 43 percent to 26 percent.
'STOP THAT JOKE'
After days of attention on his opposition to contraception and prenatal testing, Santorum touted his conservative credentials in comparison to Romney, and sought to focus on the U.S. economy, the main issue in the 2012 presidential campaign.
Santorum blasted Romney's record as a former governor of Massachusetts and said his rival's plan to cut tax rates for all Americans by 20 percent did not go far enough.
"To be attacked on television as someone who is not a true conservative by a Massachusetts governor is a joke," Santorum said in Lansing, referring to Romney's relatively moderate record in Massachusetts, a Democratic-leaning state.
"Michigan, you have the opportunity to stop that joke," he said.
In a Wall Street Journal opinion article, Santorum called for just two income tax rates and approval of the controversial Keystone oil pipeline from Canada. He vowed to make $5 trillion in budget cuts over five years.
"I'll work with Congress and the American people to once again create an economic environment where hard work is rewarded, equal opportunity exists for all, and families providing for their children can once again be optimistic about their future," he wrote.
He also vowed to repeal "all Obama administration regulations that have an economic burden over $100 million," including an Environmental Protection Agency rule on carbon emissions.
"We went into a recession in 2008 because of high gasoline prices. The bubble burst because people couldn't pay their mortgages because of four-dollar gasoline," Santorum told supporters in the state capital Lansing.
In the town of Rockford, Romney returned fire, and suggested that Santorum had spent too much time on social issues, saying: "I'm glad he recognizes this has got to be a campaign about the economy."
Romney, whose vast wealth has been an issue in the Michigan campaign, promoted himself as the candidate with the most business experience needed to trigger job growth.
"Senator Santorum is a nice guy, but he's never had a job in the private sector. He's worked as a lobbyist, worked as an elected official, and that's fine. But if the issue of the day is the economy, I think to create jobs it helps to have a guy as president who's had a job, and I have," Romney said.
In Livonia, Santorum said he was excited at his position.
"This was not a place that frankly I thought we were going to be competing at the level we're competing here in the state of Michigan," he said.
In a sign he has emerged as a leading contender, Santorum will be getting Secret Service protection beginning on Tuesday, a campaign aide told CBS News.
(Additional reporting by Sam Youngman in Michigan and Susan Heavey and Patricia Zengerle in Washington; Editing by Alistair Bell and Cynthia Osterman)