A poll worker helps U.S. President Barack Obama as he prepares to cast his vote for the 2016 U.S. presidential elections in early voting at the Cook County Office Building in Chicago, Oct. 7, 2016. Jonathan Ernst/Reuters

An analysis by the Pew Research Center indicates more than 4 million voters already had cast ballots with three weeks still to go before the general election, and if the trend continues, voters opting for convenience over heading to a polling place on Election Day could top 50 million by the time the votes all are counted.

“The greater significance of early, absentee and mail voting has prompted campaigns to shift their standard strategies, ramping up their get-out-the-vote efforts earlier and closely tracking individual voters until the moment they submit their ballots,” Pew said.

Voice of America reported more Democrats are requesting absentee ballots or voting early in swing states this year, particularly in North Carolina and Florida. Women are disproportionately represented, but it was unclear whether that would benefit Democrat Hillary Clinton or Donald Trump.

Trump has been raising the specter of widespread voter fraud without providing any evidence. Nonetheless, 14 states have changed their laws, making voting requirements more restrictive by requiring photo IDs. The fact that courts have overturned some of these laws has interjected confusion into the process.

“One of the greatest impediments to voting is confusion,” Lloyd Leonard of the League of Women Voters told PBS Newshour. “In some pretty important states the rules are still changing.”

Forty-six million voters opted for nontraditional voting methods in 2012, representing 36 percent of the electorate, according to the Pew analysis of federal and state election data, released Friday. That includes 23.3 million absentee ballots, 16.9 million early voting ballots and 6.3 million mail-in ballots.

In 2004, only 22 percent of voters opted to avoid the Election Day crush. By 2008, that proportion had grown to a third. During the last presidential election cycle, nontraditional voting methods made up more than half the vote in 12 states, including this year’s battleground states of Arizona and North California.

Oregon, Washington state and Colorado are conducting their elections totally by mail this year.

Until recently, voters had to have a good excuse for voting absentee, a process that began during the Civil War as a convenience for Union soldiers. States began experimenting with alternative methods in the 1970s and 1980s. Currently, 27 states and the District of Columbia no longer require excuses for voting absentee, compared to just 11 in 1992, Pew said.

Even seven of the 20 states that still require excuses for absentee voting offer alternatives, Pew said.

Though 21 states offer early voting, some have scaled back the number of days such balloting is allowed. Ohio reduced the number of days from 35 to 29 in 2014. North Carolina, South Dakota, Tennessee and Nebraska also have shortened the voting period.