DES MOINES — Despite early data that suggests Democrats in Iowa are lagging far behind early voting efforts in previous presidential elections, top campaign staff for Democratic candidate Hillary Clinton insist their program is working.

Campaigns encourage early voting in their attempt to maximize voter turnout. Campaign staff identify their political party’s voters and encourage them to vote early, either in person or by requesting and mailing an absentee ballot.

Democrats in recent presidential elections have emphasized the strategy in attempts to overcome Republicans’ traditionally stronger Election Day turnout. But early data shows Democrats’ 2016 early voting in Iowa is off to a comparatively slow start.

As of Thursday, Democrats in Iowa had requested 51,663 absentee ballots; that’s half the number of requests — 103,200 — made by Democrats at the same point in the 2012 presidential election.

In a conference call with Iowa reporters Thursday, Clinton’s state director and national campaign manager said they are employing a comprehensive early-voting program that stresses not just absentee ballots but also early in-person voting, as well as targeting potential supporters who in the past have not voted regularly.

“Every cycle is different, so you have to be very careful about trying to make one cycle and another apples-to-apples,” said Robby Mook, Clinton’s national campaign manager. “Our volunteers are our most precious resource, and we are trying to target their time in the most efficient way possible. So we are focused on voters who have a propensity that is lower than average to turn out.”

Mook and Kane Miller, Clinton’s state director in Iowa, said they are identifying those low-propensity voters and encouraging them to vote early in whatever method is easiest for them, whether via absentee ballot or in person.

The staff leaders said because of that strategy, their early voting numbers will improve once in-person voting starts in Iowa on Sept. 29.

“Internally, what we are tracking is how many of those low-propensity voters are turning out and what proportion of the overall turnout they constitute. We have a really good feeling on that measurement,” Mook said. “We’re trying to be very targeted in our activities here.”

Staff from both parties say they expect a close race in Iowa, making turnout efforts all the more critical for the campaigns. Most polls on the race here have shown razor-thin margins, although a recent Monmouth University Poll showed Republican Donald Trump leading Clinton by 8 percentage points, and a Quinnipiac University poll published Thursday showed Trump leading by 7 percentage points.

Miller and Mook noted Democrats still heavily outpace Republicans in absentee ballot requests. As of Thursday, Iowa Democrats had made nearly three times as many requests as Republicans.

At the same point in 2012, however, Iowa Democrats had made six times as many requests.

Iowa Republicans in 2014 started closing the early-voting gap on Democrats, and they hope to build on that momentum this fall.

“For us, the turning point was 2014 when we put resources into an absentee program. I think it’s safe to say it was the first time the Republican Party (in Iowa) took it seriously on a statewide level,” said Jeff Kaufmann, chairman of the Republican Party of Iowa. “We have the infrastructure we need. We now have the dollars thanks to the partnership with the Republican National Committee and the Trump campaign. …

“We feel like we are as prepared here as we launch into this as we’ve ever been.”