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After a half-year of fierce political competition, contentious debates, and breathless media speculation, the Iowa caucuses are finally here.

And yet, despite near-perpetual polling, it’s still not clear who will win. Competition is tight on both sides, with plenty of room for late surprises. Convincing voters to change their minds at the last minute is a fundamental part of how the Iowa caucuses are supposed to work.

As anyone who’s ever argued with family members at Thanksgiving knows, and as political science research has confirmed, it’s very hard to change people’s minds. But there are techniques that campaigns — and supporters -- can use to sway voters Monday night, taking advantage of the opportunities that caucuses provide.


How do the Iowa caucuses work?

It’s actually different for Republicans and Democrats.

At Republican caucus sites, campaign representatives get to make a final pitch, one last attempt to demonstrate the vote-worthiness of their candidate. The presentations are brief, with no time for open-ended debate, but a crisp performance could easily sway some uncertain voters.

At Democratic caucus sites, there are no opening presentations. Voters start by making a choice, dividing into groups based on whether they support Hillary Clinton, Bernie Sanders, or Martin O’Malley.

But that’s just round one in a democratic caucus. And not everyone makes it to round two. Any candidate who gets less than 15 percent of the votes in the room is eliminated — and supporters of the failed candidate have to choose anew.

Low-polling Martin O’Malley is likely to suffer this fate all over Iowa Monday, attracting a few votes at the opening but not enough to cross the 15 percent threshold. And that’s when the mind-changing will begin, as the Clinton and Sanders campaigns try to urge, persuade, cajole, and otherwise win first-round O’Malley supporters to their side for the final vote count.


What’s the best way to change minds at a caucus?

Some approaches work better than others.

It helps to start from some shared identity or perspective. If the goal is to win over veterans, let a veteran present your case. When trying to change the mind of a deeply religious voter, bond first over shared religious convictions.

This may sound narrow, or manipulative, but it has the virtue of working. And it’s a strategy that Clinton and Sanders could certainly try, tailoring their caucus message — or their messengers — to match the demographic makeup of would-be O’Malley supporters.

As an alternative, the campaigns might want to emphasize or exaggerate their current momentum.

Momentum has been a powerful factor in caucuses past, including some of the biggest upsets in Iowa history. John Kerry and John Edwards were inching up the polls in 2004, before caucus-goers sped up the process, catapulting them into the first and second spots. Likewise, George H.W. Bush was well behind but gaining ground on Ronald Reagan in 1980, until the caucuses turned that slight momentum into a sudden, winning leap.

Of course, the problem with this approach is that it only works for candidates who can point to recent good news, which at the moment means longtime leader Donald Trump and possibly Bernie Sanders, who’s been steadily gaining on Clinton.

How much can really change at the last minute?

Whether it was Kerry’s triumph in 2004 or Rick Santorum’s vault to victory in 2012, Iowa has produced its share of unexpected winners. The same could happen this year.


Not that candidates with low polling numbers, and little momentum, should expect to end up near the top. But among the leaders, even small moves could make a big difference.

For now, both the Democratic and Republican races seem close — an effective dead heat between Clinton and Sanders and a still-tight race between Trump and Cruz.

Persuasion could be the deciding factor, with the top prize going to the candidate whose caucus representatives are best prepared to woo the loosely committed. And if the result is a Sanders win or a Trump loss, that could shift the momentum of the presidential race.

And momentum really does seem to matter. Iowa’s winners haven’t always become president — witness Santorum in 2012. But candidates who beat expectations can gain long-lasting legitimacy, while those who disappoint in the Hawkeye State don’t easily recover.

Evan Horowitz digs through data to find information that illuminates the policy issues facing Massachusetts and the U.S. He can be reached at evan.horowitz@globe.com. Follow him on Twitter @GlobeHorowitz.