More than 41 million Americans had already voted as of Sunday morning, a number that is expected to surpass 2012 totals in the campaign’s closing days as more data become available.

In 2016, 37 states and the District of Columbia offered some form of early voting, whether in-person or by mail. Voters in those states could represent more than 35 percent of the total electorate, a Pew Research Center analysis estimates.

Four years ago, a third of all voters cast ballots before Election Day, a number which has increased since 1996, when just 11 percent did so.

PERCENT OF VOTES CAST EARLY

2012

30%

33%

20

10

1996

11%

0

1996

2004

2012

Source: Census Bureau

While early voting continues Monday in some places, and absentee ballots in some states will be accepted after Election Day, the totals visualized here lay out the best picture available of how the nation voted early.

This data, collected by associate professor Michael McDonald at the University of Florida in conjunction with the AP, is one of the most comprehensive sources for early-voting tallies across the country.

[ Who is winning now? Latest results from the Post-ABC presidential tracking poll]

As we mentioned in a previous graphic, the completeness of these figures hinges on how quickly the state office administering the election can process returned ballots.

The steps of “collecting these data are a real challenge, especially if the state doesn't have a centralized reporting system,” McDonald said. He estimated a third of states don’t have a centralized system that makes detailed voting data publicly available.

Sunday’s totals were about 5 million votes short of the 2012 total, but McDonald attributes that difference to incomplete reporting from state election officials at this point in the campaign.

“I'm confident that we will exceed the national total number from 2012,” he said in an email Sunday.

[ Planning to write in Paul Ryan or Bernie Sanders? It won’t count in most states.]

Another reason for low early vote totals in several states: A handful, including many in the Northeast, had little advance voting because they require a reason to vote early, such as military service or being unable to visit your polling place on Election Day.

But in some states, early voting has become the norm. Over the last 30 years, Western states have changed their voting laws to accommodate more convenient voting methods. In three — Oregon, Washington and Colorado — all voters will get ballots by mail in 2016.

Some findings from early voting data:

Hispanics in Nevada

As our colleague Philip Bump explored recently, a surge of voting in Nevada’s populous Clark County, which includes Las Vegas, seems to bode well for Clinton’s chances there.

Party registration data reinforces the Democratic ground game advantage: Democrats cast 72,000 more early votes than Republicans did.

The county contributed two-thirds of all votes in the state in 2012, handing Obama its six electoral votes.

Other states that have also seen high turnout among Hispanics include Colorado and Arizona in the West, and Texas.

[ ‘I don’t trust Mr. Crazy’: Motivated by opposition to Trump, Hispanics are poised for historic turnout]

African Americans in North Carolina

Early voting is up 12 percent in North Carolina, but warning signs have emerged for Clinton.

Black voters, a reliably Democratic group, cast 22 percent of the early votes this year, down from 27 percent in 2012 when Mitt Romney edged out a win there.

That change is attributable to both a lack of enthusiasm, but also a surge in white voters, which should boost Donald Trump’s totals.

[ What one swing state can teach us about political polarization in America]

D.C., Maryland and Virginia

Maryland saw a 68 percent spike in early voting since 2012, with the overwhelming majority of voters being Democrats.

Advance voting also ticked up in more competitive Virginia, though the state requires an excuse to vote before Election Day. Much of the increase came in Northern Virginia, which bodes well for Clinton’s chances in the state.

Early voting in the District grew by 47 percent.

As early voting becomes the method of choice for millions more voters every four years, Election Day is no longer concentrated on a single Tuesday in November, but in the several weeks leading up to that day. While we won’t know who early voters supported until Tuesday, their increasing importance across the country in key battleground states is clear.

Update: A reader pointed out a problem with the Texas totals that speaks to the limitations of data collection. At this point in the election, early voting in the 15 counties where Texas reports totals has increased. However, these 15 counties fall short of the entire state’s 2012 early voting totals. A more complete picture will emerge once more data is available.

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