The trend is also evident in early vote data from other swing states that could play key roles in deciding the election, including Florida and Georgia.
More Latino voters, however, are among the more than 24.4 million American voters who have already cast their ballots -- including 12.4 million in battleground states -- according to a CNN analysis of the latest early voting numbers.
Republicans appear to be in better position than they were in previous presidential elections in Florida, Iowa, North Carolina and Ohio, while Democrats have improved their standing in Colorado and Arizona.
CNN has partnered with Catalist, a data company that works with progressive candidates and groups, to receive detailed early vote return information this year. Catalist's voter list connects returned ballots with demographic and registration information, such as party registration, gender and age, and allows a closer look at who has already cast a vote.
These are not results -- ballots aren't tallied until Election Day. But the findings provide clues on who is voting and which party is turning out to vote. And while the numbers track voters' party affiliations, not all Democrats are voting for Hillary Clinton, and not all Republicans are supporting Donald Trump.
Here's a look at the early voting data from several battleground states:
Democrats still lag Republicans by about 40,000 early votes so far in Arizona, but that's less today than the 70,000-vote lead Republicans held at this point in 2012. That difference means the GOP's 10% edge in 2012 is a 4% edge now, with more than 1 million ballots cast.
That 10% early vote margin largely matched the size of Mitt Romney's victory -- which suggests Clinton's campaign appears to have a fighting chance to flip the state.
Two-thirds of Arizona voters cast their ballots before Election Day in 2012 -- making these early voting numbers crucial to watch for Clinton and Trump.
Despite Trump's late move to turn the state competitive, Democrats remain ahead in ballot returns in the entirely vote-by-mail state.
Of the more than 1 million Coloradoans who have voted so far, Democrats have a lead of 2.4 percentage points. At this point four years ago, the GOP had 2.8-point edge, and that ultimately wasn't enough for Romney to carry the state.
However, there's some good news for Republicans: As more ballots are counted, the size of the Democratic lead is shrinking -- with the party's advantage remaining at about 24,000 votes for the past week.
Republicans hope a simple mail delay in returns from the state's rural counties, compared with quicker delivery from Denver, will ultimately narrow the gap.
Registered Republicans have a very narrow lead in Florida early voting. They're up by about 8,800 votes, which is a better position than they were in eight years ago, when they trailed registered Democrats by about 50,000.
Helping the GOP: The burst in Democratic turnout two weekends before Election Day in 2008 does not appear to have materialized this year.
The demographics of Florida's have also changed since 2008. The white vote has remained about 72%. But the black vote has dipped from 15% in 2008 to 12% this year. Latinos have boosted their share of the vote from 9.4% in 2008 to 14% today.
In each of the two previous presidential races, more than half of Florida's electorate voted early. The early vote share was 56% in 2012, and that number is expected to continue climbing in 2016.
About 1.5 million ballots have been cast in Georgia -- a 28% increase compared to 2008 and a 32% bump over 2012, when half the state voted early.
The Peach State doesn't register voters by party, so it's impossible to know whether more Democrats or Republicans have voted.
But if Clinton is going to pull off the upset here, she'll need strong turnout from African-Americans -- and there are signs that their share of the vote has dropped a bit from where it was at this point in 2012. Black voters made up 36% of Georgia's early voting population at this stage of the 2012 race, compared to 31% this year.
Democrats are ahead among the 448,000 votes cast so far in Iowa -- but they're still behind the party's 2012 pace in a state that Clinton's campaign has long admitted will be tough to win.
Democrats led by 58,000 votes, an edge of nearly 12%, at this point in 2012. Today, they are up by nearly 42,000, or 9.3%. That's a drop in the Democratic lead of about 5 points over the last week.
Overall early vote numbers in Iowa are down, as well, from 491,000 ballots cast at this point in 2012.
Overall turnout in Nevada lags behind 2012 -- with 420,000 ballots cast so far in 2016, compared to 460,000 at this point four years ago. But the Democratic advantage in a state Obama carried appears to have held.
Democrats lead by about 32,000 votes -- 7.5 points ahead of Republicans, roughly where they were in 2012. And the Democratic lead has grown in recent days.
Nevada is a crucial early voting state. In 2012, 69% of the state's electorate cast their ballots before Election Day.
For the first time this cycle, Democrats are ahead by more than 200,000 early votes, and they have a 13.4-percentage-point lead over Republicans. But that's still off the party's 2012 pace in a state Romney narrowly won: Four years ago, Democrats were up by 292,000 votes at this stage, or 17.9 points.
The black vote is also down in the Tar Heel State. At this point in 2012, the electorate was 67% white and 28% black. Today, it is 73% white and 23% black.
The Latino vote has ticked upward in North Carolina, from 1.1% at this point in 2012 to 1.8% in 2016.
North Carolina reduced its early voting window, but the total ballots cast so far slightly outpace 2012 -- when 61% of the vote was cast early.
Republicans continue to outperform their results from 2008, the last year with comparable results. The GOP has an edge over Democrats of 4.7% now, while Democrats held a very slight lead at this stage in 2008.
So far, nearly 1.2 million votes have been cast in Ohio -- a drop of about 13,000 from 2012.
After the last presidential election, Ohio's Republican-controlled legislature slashed back the number of early voting days. There are some signs that the drop-off has been heavier in Democratic-leaning counties, bad news for Clinton.