RENEE MONTAGNE, HOST:
For most Americans, Election Day is November 8. Though starting today, voters in the key swing state of Iowa can cast their ballots. Iowa is one of many states providing the option of voting early.
As NPR's Scott Detrow reports, this creates strategic opportunities for the campaigns.
SCOTT DETROW, BYLINE: More than 3 in 10 voters are expected to cast their ballots before Election Day.
MICHAEL MCDONALD: In some of the other states, some of the key battleground states like a Florida, North Carolina, Colorado, Nevada, we'll see two-thirds, maybe more of the votes cast prior to Election Day.
DETROW: Michael McDonald is a political science professor at the University of Florida. He's an expert on early voting.
As voters cast their ballots, they'll provide a glimpse of how the election is shaping up. Campaigns are keeping track of how many Democrats or Republicans have asked for or turned in early ballots. Those figures can indicate voter enthusiasm.
But McDonald says it's important to be cautious about all this information, and how it's spun - especially right away. He says there are big picture trends to keep in mind because Republicans tend to bank larger numbers early on.
MCDONALD: Republicans should be doing better in the mail ballots than the Democrats. As - when we get closer to Election Day, especially around the two weeks prior to the election, that's when in-person early voting will start. And at that stage, we're going to see a flood of Democrats start coming into the electorate.
DETROW: Still, there's a lot here for campaigns to take in and act on.
Now, campaigns don't know who these people are voting for, but they think they've got a pretty good idea. Campaigns have been gathering information about likely supporters all year - what issues they care about, how likely they are to vote, things like that. Now is the time when campaigns get in touch and do their best to steer voters to the polls.
Paul Mitchell is a California political strategist who tracks voter data. He says the more supporters a campaign can convince to vote early, the easier its job becomes.
PAUL MITCHELL: Because if you can get your voters to turn in their ballots earlier, you essentially take that job you have of getting out the vote and reduce it by having gotten them to vote earlier.
DETROW: And, Mitchell says, the more information a campaign has about who exactly has turned in their ballots, the more efficient it can be with limited time and money.
MITCHELL: If they're marked in your voter file as having voted, you don't have to send them a single mail or you don't have to make a single phone call. You do not have to put a Facebook ad up on them.
DETROW: This is what's happening in Iowa right now, as voters begin returning ballots in the mail and showing up at early voting sites.
Typically, Iowa Democrats have outgunned Republicans when it comes to rounding up supporters and making sure they vote before Election Day. The GOP is working hard to close that gap this year, says state Republican chair Jeff Kaufmann. He says up to half of Republican ballots could be cast early because of the party's aggressive outreach.
JEFF KAUFMANN: We're taking a page out of the Obama playbook. And we are going to put feet on the ground.
DETROW: Right now, more Democrats have requested early ballots than Republicans. But so far, those numbers lag far behind where the party was four years ago. Democrats say they're focusing on rounding up voters who have a spottier track record of showing up on Election Day.
President Obama won Iowa twice, but right now Donald Trump leads in the polls. So finding those low-turnout Democrats and banking their votes could be the difference between a Trump and Clinton win in the key swing state.
Scott Detrow, NPR News. Transcript provided by NPR, Copyright NPR.