Des Moines, Iowa (CNN) -- With five days to go until the caucuses, a new poll is really shaking things up in Iowa.
Six of the major Republican presidential candidates are barnstorming across Iowa on Thursday against a changing political landscape -- a CNN/Time/ORC International poll released Wednesday showed support plunging for former House Speaker and onetime front-runner Newt Gingrich while onetime longshot Rick Santorum surged into the top three.
Santorum, campaigning on a shoestring budget, joked Wednesday night at a campaign event in Cedar Rapids that his bus "is a truck." But he has visited all of Iowa's 99 counties and he said his relentless efforts are paying dividends.
"It's like any small-business person," he told CNN's Wolf Blitzer on "The Situation Room" on Wednesday. "If the money's not coming in, you've just got to work harder, and that's what we're doing.
"We're going up in the morning doing radio shows at 6 in the morning and going until 9, 10 at night and town meeting after town meeting. ... Hard work pays off."
In the Wednesday poll, 25% of those questioned said that if the January 3 caucuses were held today, they most likely would back former Massachusetts Gov. Mitt Romney, with 22% saying they'd support Rep. Ron Paul of Texas. Romney's 3-point margin is within the poll's sampling error.
Both Romney and Paul were each up 5 points among likely caucus-goers from a CNN/Time/ORC poll conducted at the start of December. The new survey indicated that Santorum, the former senator from Pennsylvania, is at 16% support, up 11 points from the beginning of the month, with Gingrich at 14%, down 19 points.
Santorum starts Thursday with what his campaign calls a "Faith, Family, and Freedom" town hall in Coralville. He has made a strong pitch toward social conservative voters, who are very influential among Iowa Republicans.
On Wednesday, Santorum was up with a new radio spot on Hawkeye State airwaves touting endorsements by social conservative leaders. His pitch may be starting to pay off.
"Most of Santorum's gains have come among likely caucus participants who are born-again or evangelical, and he now tops the list among that crucial voting bloc, with support from 22% of born-agains compared to 18% for Paul, 16% for Romney, and 14% for Gingrich," said CNN polling director Keating Holland.
It's a different story for Gingrich, who starts Thursday with a campaign stop in Sioux City. Since Gingrich's rise late last month and early this month in both national and early voting state surveys, he has come under fire from many of the rival campaigns. And his campaign blames the onslaught for the drop in the polls.
"Iowa's a very small media market. You can basically blanket the airwaves if you have enough money. And I don't care what candidate is in the race, if you have $9 million in negative advertising against them, (they are) going to drop in the polls," Gingrich communications director Joe DeSantis told CNN's Candy Crowley on "John King, USA" on Wednesday.
Rep. Michele Bachmann of neighboring Minnesota starts Thursday with a radio interview in Des Moines, and then speaks to reporters. She was at 9% support in the new CNN poll, trailing Texas Gov. Rick Perry by 2 percentage points. Wednesday night her state chairman abandoned ship -- state Sen. Kent Sorenson showed up at a rally for Paul and backed the longtime congressman, telling the crowd that "I believe we are in a turning point in this campaign."
Perry, like Santorum and Bachmann, is making a major effort to court social conservatives. A day after announcing his position on abortion had undergone a "transformation," Perry sought to clarify that he would allow for exceptions if a mother's life was in danger. On Tuesday, Perry told a crowd in Iowa that he had toughened his stance on abortion after viewing a documentary produced by former Arkansas Gov. Mike Huckabee, who won here in 2008 before later abandoning his presidential bid. Perry said he had changed his position to oppose abortion, even in cases of rape or incest.
As for the two front-runners, Romney is expected to emphasize jobs and the economy as he meets with voters in Cedar Falls. Paul begins his day of campaigning with a radio interview in Des Moines.
CNN's Shannon Travis, Lisa Desjardins and Kevin Liptak contributed to this report.