Members of Occupy Wall Street and various labour groups hold a protest against Republican presidential candidate Mitt Romney in New York City
Republican White House hopefuls set their sights on President Barack Obama's home state of Illinois Friday in hopes of shaking up the plodding race to become their party's standard bearer in the November election, reports AFP.
Conservative darling Rick Santorum is aiming for another come-from-behind victory as polls showed he is in striking distance of frontrunner Mitt Romney, who has a commanding lead in all-important delegates but has been weakened by his failure to clinch the deal.
A win in this midwestern, industrialized state Tuesday would prove a far more significant upset than Santorum's recent victory in the Deep South states of Alabama and Mississippi, where evangelical voters carry more weight.
It would also give Santorum important momentum going into the southern state of Louisiana's primary on March 24 and contests in Wisconsin, Maryland and Washington on April 3.
The former Pennsylvania senator is making an aggressive push in Illinois, adding multiple campaign stops and launching ads attacking Romney for raising taxes and supporting the Wall Street bailout and a government take-over of healthcare.
"It's time conservatives take a stand," Santorum said in a fundraising note to supporters Thursday.
"I am convinced that whoever can activate grassroots activists will not only win the nomination but have the honor of defeating Barack Obama."
Romney has responded to the threat by moving up plans to campaign in Illinois -- squeezing in an appearance early Friday before he flies to Puerto Rico ahead of caucuses there Sunday -- and pouring millions of dollars in ads onto the Illinois airwaves.
"I've got a real strong lead and that's because I've gotten a million more votes than Rick Santorum has," Romney told Fox News Thursday.
"The reason that's happened is because I've been talking about the economy and getting people back to work."
Obama waded into the race Thursday, mocking Republicans who oppose his energy plans as "naysayers" on a day his reelection campaign stepped up a notch with the release of a laudatory documentary on his presidency.
Vice President Joe Biden threw even sharper barbs during a major campaign swing in the crucial battleground state of Ohio where he called out the remaining Republican contenders by name.
"If you give any one of these guys the keys to the White House, they will bankrupt the middle class again," Biden told a crowd of union workers.
"The president and I have a fundamental commitment to dealing the middle class back into the American economy that they have been dealt out of so long. And ultimately that's what this election is all about. It's about a choice.
"A choice between a system that is rigged and a system that is fair.
"It's a stark choice. To my mind it's not even a close call."
The campaign's new intensity comes at a moment of high volatility in American politics, with Obama's approval rating lurching up and down in several polls, partly influenced by rising gasoline prices.
Senior Obama administration officials dismissed a New York Times/CBS poll this week which put Obama's job approval rating at 41 percent, down from 50 percent a month ago.
But they concede that Obama will face a tough fight in November, in a country that is split down the middle ideologically, with the outcome likely to rest on the state of the economy.
The increasingly divisive Republican race has been an unexpected boon for Obama and it could continue for weeks if not months to come.