SIOUX CITY, Iowa — Iowa caucus-goers – like their fellow first-in-the-nation voters in New Hampshire – are notoriously wary of being told who to support on caucus day.

Former Pennsylvania senator Rick Santorum, now surging in the polls, is trying to tap into that sentiment.

View Photo Gallery: The PostPolitics team used the iPhone app Instagram and the tag #2012Unfiltered to document the week leading up to the Iowa caucuses.

As he continues his final campaign sprint with just two days to go until the caucuses, Santorum is making his pitch to voters by asking them to trust their own judgment – not telling them how to vote.

“Don’t pay attention to what the national pundits are saying as to who you need to vote for to win the race,” Santorum told a crowd at the Indianola Public Library Saturday afternoon. “I understand they’re saying, you know, who can win and who cannot. Trust your own heart. Trust your head. Trust your gut as to who you believe is best. You fight to be the first in the nation. ... Trust your judgment and lead.”

Santorum, unlike Texas Gov. Rick Perry (R) and Rep. Ron Paul (R-Texas), has not flooded the Iowa airwaves. He reminded voters Saturday that he remains a fundraising underdog.

Instead, he appealed to Iowa caucus-goers’ sense that their nominating contest not only helps winnow the field, but that it can be a transformative process for candidates as well.

“I will forever be a fan and a defender of the Iowa caucuses, because it does make you a better candidate,” he said. “I think it makes you think about not just what you’re saying and how you’re saying it, but think about why you’re saying it. ... I would say to any candidate who’s going to run for president, again, don’t pass up the opportunity. It will make you not only a better candidate; it will make you a better president; and it certainly made me and my family better people.”

A Des Moines Register poll released late Saturday shows Santorum surging – and also reveals that 41 percent of likely GOP voters could change their minds ahead of Tuesday’s caucuses.

It’s with an eye toward those more than four-in-ten undecideds that Santorum is making his final pitch. As Rep. Steve King (R-Iowa) explained in a phone interview Friday, what’s exceptional about Iowa’s caucus system -- as opposed to a primary – is that it’s a process of active deliberation, one in which voters very often come to a final decision only after debating with their neighbors at the caucus itself.

“It’s pretty rare to walk into a room, be it a committee room or the full chamber of the House or the Senate, and have somebody make up their mind how they’re going to vote once the meeting starts,” said King, who has remained neutral so far in the GOP race. “Not in the Iowa caucus. Many, many activists go there to objectively listen to the speeches and make up their mind inside the caucus room.”

Romney, who polls show is holding onto a slim lead over Rep. Ron Paul (R-Texas) in the Hawkeye State, has also taken an “ask, don’t tell” approach on the trail. But that message has been blunted somewhat by his argument that he will be the most electable candidate come November.

“I sure hope that I become the nominee,” Romney told a Sioux City crowd Saturday night, hours before ringing in the new year. “I know that the battle for the soul of America’s going to begin on Tuesday evening, and I hope that you get out and caucus and give me your support. But I can tell you this: If I’m your nominee, I will be back in the general election and we will win Iowa and take back the White House with the support of this great state.”

Both Romney and Santorum have been winning over their share of undecideds in recent days, and Romney on the trail has appeared confident in his standing in the polls. But if Santorum manages to eke out a come-from-behind win two days from now, it may well be because his “ask, don’t tell” message has resonated more strongly with voters.

“He didn’t tell me to vote for him,” said Reah Adamson, 62, who arrived at Santorum’s Indianola event as undecided and left as an enthusiastic Santorum backer. “He said, ‘Trust yourself. Trust your instincts.’ That’s exactly why I was here today. I was here today so that I could get the instinct or the feel that I needed to get the, ‘Okay, I’m going to caucus for you.’ And I got that.”

Today on the trail (Courtesy of the PBS NewsHour Political Calendar and campaign advisories; all times Eastern):

9 a.m.: Rep. Ron Paul (R-Tex.), Rep. Steve King (R-Iowa) and Iowa Gov. Terry Branstad (R) appear on CNN’s “State of the Union.”

9 a.m.: Rep. Ron Paul (R-Tex.), Texas Gov. Rick Perry (R), Rep. Michele Bachmann (R-Minn.) and Iowa Gov. Terry Branstad (R) appear on “Fox News Sunday.”

10 a.m.: Rep. Michele Bachmann (R-Minn.), Rep. Ron Paul (R-Tex.) and Iowa Gov. Terry Branstad (R) appear on ABC’s “This Week.”

10:30 a.m.: Former senator Rick Santorum (R-Pa.), Iowa GOP chairman Matt Strawn and Iowa Gov. Terry Branstad (R) appear on NBC’s “Meet the Press.”

10:30 a.m.: Sen. Rand Paul (R-Ky.), former senator Jim Talent (R-Mo.) and former Rep. J.C. Watts (R-Okla.) appear on CBS’s “Face the Nation.”

1 p.m.: Former House speaker Newt Gingrich holds a campaign event at the West Towne Pub in Ames, Iowa.

3 p.m.: Newt Gingrich holds an event at the Junction Sports Bar & Grill in Marshalltown, Iowa.

3:15 p.m.:Former Massachusetts governor Mitt Romney meets with voters at the Family Table Restaurant in Atlantic, Iowa.

3:30 p.m.: Rick Santorum holds a campaign event at the Daily Grind in Sioux City, Iowa.

5:30 p.m.: Newt Gingrich holds a campaign event at LJ’s Neighborhood Bar and Grill in Waterloo, Iowa.

5:45 p.m.: Rick Santorum holds a campaign rally at Northwestern Bank in Orange City, Iowa.

6:05 p.m.: Mitt Romney holds a rally at the Bayliss Park Hall in Council Bluffs, Iowa.

7:30 p.m.: Rick Santorum holds a campaign rally in Rock Rapids, Iowa.