In Iowa's quirky caucus system, a candidate who works to be the second choice can end up finishing first.

It's a counterintuitive strategy, but one that has worked in the past and is being stressed by several Democratic candidates this year.

"You have to understand how a caucus works," said Teresa Vilmain, who is heading Hillary Rodham Clinton's Iowa campaign.

The key is a Democratic rule that candidates need the backing of at least 15 percent of people at a caucus meeting for that support to count. If a candidate doesn't achieve the 15 percent viability rule, the candidate's supporters can switch to their second choice or call it quits.

Republicans don't have such a rule and choose candidates by secret ballot.

Democratic frontrunners Clinton, Barack Obama and John Edwards are trying to establish themselves as second options to the other candidates. The assumption is that the candidates leading in Iowa polls will easily meet the viability rule, but in many of Iowa's 1,784 precincts backers of Democrats such as Joe Biden, Bill Richardson or Chris Dodd may have to make a choice.

"Clearly Obama and Hillary are going to be viable everywhere," said veteran activist Joe Shannahan. "If you identify Richardson supporters and Biden supporters, it's a good strategy to court them now."

Obama campaign organizers said they're doing just that.

"During the course of a conversation, if they say they are supporting someone else, we ask if we can be their second choice," said Paul Tewes, who is running Obama's Iowa campaign. "This happens in pretty much every conversation."

Anne Heinz of Dubuque has heard the pitch. She's a strong supporter of Joe Biden, and held a house party for the Delaware senator. But she's also a realist and thinks he might not be viable at her precinct caucus meeting.

If that's the case, her support would shift to Clinton.

"She would be my second choice because she's got a lot of moxie," Heinz said. "I think she's got a lot going and she's a very bright woman. I would be very comfortable moving to her."

Given the often chaotic nature of the caucuses — police have been called to gatherings in past years to calm disputes — campaigns want to fine tune their strategies early. Democratic caucuses are famous for horse-trading that begins after the initial preference breakdown, with activists offering platform planks or other promises in exchange for delegate support.

Vilmain, whose caucus-organizing experience dates back to the 1988 campaign of Michael Dukakis, said a key is to recruit and train backers in each precinct who understand the process and can take charge of a community meeting.

"We're in the process of locking down the precinct captains," said Vilmain. "You have to have people in the room who are trained and well-equipped, people who have done this before."

She said one reason Al Gore trounced Bill Bradley in the 2000 campaign was because his campaign had focused on attracting undecided voters and those supporting back-of-the-pack candidates.

"I think some of the lessons are that everybody has to understand what second choices are," said Vilmain.

In 2004, a factor in Edwards' surprising second place finish was his quiet courting of Ohio Rep. Dennis Kucinich's backers, said Jeff Link, an Edwards adviser.

The second-choice effort could be especially important this year because polls show Iowa Democrats are pleased with the field of candidates and could accept switching if their favorites aren't viable.

Link said many activists may have to choose a second option, noting.

"You could have three campaigns who are not viable in a precinct."